java double assignment

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What is the difference/ advantage of doing double assignment?

Is there any advantage / is it a bad practice in Java to do the below

I saw it in one of my peers code and I was surprised why he would do double assignment?

Is this something that is same as x = 5 or if x = x= 5 makes a difference?

• 8 Did you actually see x = x = 5 , or was it more like x = y = 5 ? The second one makes sense, but the first one is just weird. –  Tacroy Commented Jul 16, 2013 at 17:54
• 14 Wouldn't call it a bad practice, it has more of an insanity vibe to it. Consider moving your desk farther from his. –  ZJR Commented Jul 16, 2013 at 18:20
• 3 Are you sure it's not a cut & paste error? There's an apparently not-so-famous (since I can't find a link) quote that says "when you see someone you respect deep in thought, chances are he's thinking about lunch". You should ask him about it. –  Dan Pichelman Commented Jul 16, 2013 at 18:26
• 4 @rao: How you word the question can create a different tone. "Why did you write that? It doesn't make sense." would put the programmer on the defensive. However, asking for clarification about what the line does opens the door more gently. If the description does not make sense, then you should come out an discuss how each of you have different understands of what is being done and what should be done. Your job is to make the code better, programmers should not be offended when an actual bug is found in their code. –  unholysampler Commented Jul 16, 2013 at 18:26
• 3 This one is simply a nonsense, period. –  Pavel Horal Commented Jul 16, 2013 at 19:18

Is there any advantage/ is it a bad practice to do the below x= x = 5

You haven't specified the language, but in most C-like languages the value of an assignment is the value being assigned. That is, the value of the expression x = 5 is 5 , and the expression you're asking about is essentially the same as doing:

There's no value in the extra assignment, so no reason to do it.

Now, what you do sometimes see is the assignment of two (or more) variables to some value at the same time, like this:

In this case, you're assigning 5 to y , and then assigning the value of that expression (again, 5) to x . This ensures that both x and y get the same value.

Another possibility is that one of the assignments was intended to be a comparison, with the result assigned to the variable being compared:

This isn't a double assignment, it's assignment of the boolean expression x == 5 to x . That is, if the value of x is 5 before the expression, x will get the value of true (some non-zero integer); if x is not 5, x will be set to false (i.e. 0).

• The language I am referring is Java, thanks for the clarification. –  rao Commented Jul 16, 2013 at 17:59
• 3 x = x == 5 works in C, but (thankfully!) not in Java :) –  Andres F. Commented Jul 16, 2013 at 18:30
• 1 @AndresF. Agree, and since we now know that the OP is talking about Java, the last part of my answer really doesn't apply. –  Caleb Commented Jul 16, 2013 at 18:34

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• Scratch ActiveCode
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• 1.1 Preface
• 1.2 Why Programming? Why Java?
• 1.3 Variables and Data Types
• 1.4 Expressions and Assignment Statements
• 1.5 Compound Assignment Operators
• 1.6 Casting and Ranges of Variables
• 1.7 Java Development Environments (optional)
• 1.8 Unit 1 Summary
• 1.9 Unit 1 Mixed Up Code Practice
• 1.10 Unit 1 Coding Practice
• 1.11 Multiple Choice Exercises
• 1.12 Lesson Workspace
• 1.3. Variables and Data Types" data-toggle="tooltip">
• 1.5. Compound Assignment Operators' data-toggle="tooltip" >

1.4. Expressions and Assignment Statements ¶

In this lesson, you will learn about assignment statements and expressions that contain math operators and variables.

1.4.1. Assignment Statements ¶

Remember that a variable holds a value that can change or vary. Assignment statements initialize or change the value stored in a variable using the assignment operator = . An assignment statement always has a single variable on the left hand side of the = sign. The value of the expression on the right hand side of the = sign (which can contain math operators and other variables) is copied into the memory location of the variable on the left hand side.

Figure 1: Assignment Statement (variable = expression) ¶

Instead of saying equals for the = operator in an assignment statement, say “gets” or “is assigned” to remember that the variable on the left hand side gets or is assigned the value on the right. In the figure above, score is assigned the value of 10 times points (which is another variable) plus 5.

The following video by Dr. Colleen Lewis shows how variables can change values in memory using assignment statements.

As we saw in the video, we can set one variable to a copy of the value of another variable like y = x;. This won’t change the value of the variable that you are copying from.

Click on the Show CodeLens button to step through the code and see how the values of the variables change.

The program is supposed to figure out the total money value given the number of dimes, quarters and nickels. There is an error in the calculation of the total. Fix the error to compute the correct amount.

Calculate and print the total pay given the weekly salary and the number of weeks worked. Use string concatenation with the totalPay variable to produce the output Total Pay = $3000 . Don’t hardcode the number 3000 in your print statement.

Assume you have a package with a given height 3 inches and width 5 inches. If the package is rotated 90 degrees, you should swap the values for the height and width. The code below makes an attempt to swap the values stored in two variables h and w, which represent height and width. Variable h should end up with w’s initial value of 5 and w should get h’s initial value of 3. Unfortunately this code has an error and does not work. Use the CodeLens to step through the code to understand why it fails to swap the values in h and w.

1-4-7: Explain in your own words why the ErrorSwap program code does not swap the values stored in h and w.

Swapping two variables requires a third variable. Before assigning h = w , you need to store the original value of h in the temporary variable. In the mixed up programs below, drag the blocks to the right to put them in the right order.

The following has the correct code that uses a third variable named “temp” to swap the values in h and w.

The code is mixed up and contains one extra block which is not needed in a correct solution. Drag the needed blocks from the left into the correct order on the right, then check your solution. You will be told if any of the blocks are in the wrong order or if you need to remove one or more blocks.

After three incorrect attempts you will be able to use the Help Me button to make the problem easier.

Fix the code below to perform a correct swap of h and w. You need to add a new variable named temp to use for the swap.

1.4.2. Incrementing the value of a variable ¶

If you use a variable to keep score you would probably increment it (add one to the current value) whenever score should go up. You can do this by setting the variable to the current value of the variable plus one (score = score + 1) as shown below. The formula looks a little crazy in math class, but it makes sense in coding because the variable on the left is set to the value of the arithmetic expression on the right. So, the score variable is set to the previous value of score + 1.

Click on the Show CodeLens button to step through the code and see how the score value changes.

1-4-11: What is the value of b after the following code executes?

• It sets the value for the variable on the left to the value from evaluating the right side. What is 5 * 2?
• Correct. 5 * 2 is 10.

1-4-12: What are the values of x, y, and z after the following code executes?

• x = 0, y = 1, z = 2
• These are the initial values in the variable, but the values are changed.
• x = 1, y = 2, z = 3
• x changes to y's initial value, y's value is doubled, and z is set to 3
• x = 2, y = 2, z = 3
• Remember that the equal sign doesn't mean that the two sides are equal. It sets the value for the variable on the left to the value from evaluating the right side.
• x = 1, y = 0, z = 3

1.4.3. Operators ¶

Java uses the standard mathematical operators for addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). Arithmetic expressions can be of type int or double. An arithmetic operation that uses two int values will evaluate to an int value. An arithmetic operation that uses at least one double value will evaluate to a double value. (You may have noticed that + was also used to put text together in the input program above – more on this when we talk about strings.)

Java uses the operator == to test if the value on the left is equal to the value on the right and != to test if two items are not equal. Don’t get one equal sign = confused with two equal signs == ! They mean different things in Java. One equal sign is used to assign a value to a variable. Two equal signs are used to test a variable to see if it is a certain value and that returns true or false as you’ll see below. Use == and != only with int values and not doubles because double values are an approximation and 3.3333 will not equal 3.3334 even though they are very close.

Run the code below to see all the operators in action. Do all of those operators do what you expected? What about 2 / 3 ? Isn’t surprising that it prints 0 ? See the note below.

When Java sees you doing integer division (or any operation with integers) it assumes you want an integer result so it throws away anything after the decimal point in the answer, essentially rounding down the answer to a whole number. If you need a double answer, you should make at least one of the values in the expression a double like 2.0.

With division, another thing to watch out for is dividing by 0. An attempt to divide an integer by zero will result in an ArithmeticException error message. Try it in one of the active code windows above.

Operators can be used to create compound expressions with more than one operator. You can either use a literal value which is a fixed value like 2, or variables in them. When compound expressions are evaluated, operator precedence rules are used, so that *, /, and % are done before + and -. However, anything in parentheses is done first. It doesn’t hurt to put in extra parentheses if you are unsure as to what will be done first.

In the example below, try to guess what it will print out and then run it to see if you are right. Remember to consider operator precedence .

1-4-15: Consider the following code segment. Be careful about integer division.

What is printed when the code segment is executed?

• 0.666666666666667
• Don't forget that division and multiplication will be done first due to operator precedence.
• Yes, this is equivalent to (5 + ((a/b)*c) - 1).
• Don't forget that division and multiplication will be done first due to operator precedence, and that an int/int gives an int result where it is rounded down to the nearest int.

1-4-16: Consider the following code segment.

What is the value of the expression?

• Dividing an integer by an integer results in an integer
• Correct. Dividing an integer by an integer results in an integer
• The value 5.5 will be rounded down to 5

1-4-17: Consider the following code segment.

• Correct. Dividing a double by an integer results in a double
• Dividing a double by an integer results in a double

1-4-18: Consider the following code segment.

• Correct. Dividing an integer by an double results in a double
• Dividing an integer by an double results in a double

1.4.4. The Modulo Operator ¶

The percent sign operator ( % ) is the mod (modulo) or remainder operator. The mod operator ( x % y ) returns the remainder after you divide x (first number) by y (second number) so 5 % 2 will return 1 since 2 goes into 5 two times with a remainder of 1. Remember long division when you had to specify how many times one number went into another evenly and the remainder? That remainder is what is returned by the modulo operator.

Figure 2: Long division showing the whole number result and the remainder ¶

In the example below, try to guess what it will print out and then run it to see if you are right.

The result of x % y when x is smaller than y is always x . The value y can’t go into x at all (goes in 0 times), since x is smaller than y , so the result is just x . So if you see 2 % 3 the result is 2 .

1-4-21: What is the result of 158 % 10?

• This would be the result of 158 divided by 10. modulo gives you the remainder.
• modulo gives you the remainder after the division.
• When you divide 158 by 10 you get a remainder of 8.

1-4-22: What is the result of 3 % 8?

• 8 goes into 3 no times so the remainder is 3. The remainder of a smaller number divided by a larger number is always the smaller number!
• This would be the remainder if the question was 8 % 3 but here we are asking for the reminder after we divide 3 by 8.
• What is the remainder after you divide 3 by 8?

1.4.5. FlowCharting ¶

Assume you have 16 pieces of pizza and 5 people. If everyone gets the same number of slices, how many slices does each person get? Are there any leftover pieces?

In industry, a flowchart is used to describe a process through symbols and text. A flowchart usually does not show variable declarations, but it can show assignment statements (drawn as rectangle) and output statements (drawn as rhomboid).

The flowchart in figure 3 shows a process to compute the fair distribution of pizza slices among a number of people. The process relies on integer division to determine slices per person, and the mod operator to determine remaining slices.

Figure 3: Example Flow Chart ¶

A flowchart shows pseudo-code, which is like Java but not exactly the same. Syntactic details like semi-colons are omitted, and input and output is described in abstract terms.

Complete the program based on the process shown in the Figure 3 flowchart. Note the first line of code declares all 4 variables as type int. Add assignment statements and print statements to compute and print the slices per person and leftover slices. Use System.out.println for output.

1.4.6. Storing User Input in Variables ¶

Variables are a powerful abstraction in programming because the same algorithm can be used with different input values saved in variables.

Figure 4: Program input and output ¶

A Java program can ask the user to type in one or more values. The Java class Scanner is used to read from the keyboard input stream, which is referenced by System.in . Normally the keyboard input is typed into a console window, but since this is running in a browser you will type in a small textbox window displayed below the code. The code below shows an example of prompting the user to enter a name and then printing a greeting. The code String name = scan.nextLine() gets the string value you enter as program input and then stores the value in a variable.

Run the program a few times, typing in a different name. The code works for any name: behold, the power of variables!

Run this program to read in a name from the input stream. You can type a different name in the input window shown below the code.

Try stepping through the code with the CodeLens tool to see how the name variable is assigned to the value read by the scanner. You will have to click “Hide CodeLens” and then “Show in CodeLens” to enter a different name for input.

The Scanner class has several useful methods for reading user input. A token is a sequence of characters separated by white space.

Run this program to read in an integer from the input stream. You can type a different integer value in the input window shown below the code.

A rhomboid (slanted rectangle) is used in a flowchart to depict data flowing into and out of a program. The previous flowchart in Figure 3 used a rhomboid to indicate program output. A rhomboid is also used to denote reading a value from the input stream.

Figure 5: Flow Chart Reading User Input ¶

Figure 5 contains an updated version of the pizza calculator process. The first two steps have been altered to initialize the pizzaSlices and numPeople variables by reading two values from the input stream. In Java this will be done using a Scanner object and reading from System.in.

Complete the program based on the process shown in the Figure 5 flowchart. The program should scan two integer values to initialize pizzaSlices and numPeople. Run the program a few times to experiment with different values for input. What happens if you enter 0 for the number of people? The program will bomb due to division by zero! We will see how to prevent this in a later lesson.

The program below reads two integer values from the input stream and attempts to print the sum. Unfortunately there is a problem with the last line of code that prints the sum.

Run the program and look at the result. When the input is 5 and 7 , the output is Sum is 57 . Both of the + operators in the print statement are performing string concatenation. While the first + operator should perform string concatenation, the second + operator should perform addition. You can force the second + operator to perform addition by putting the arithmetic expression in parentheses ( num1 + num2 ) .

More information on using the Scanner class can be found here https://www.w3schools.com/java/java_user_input.asp

1.4.7. Programming Challenge : Dog Years ¶

In this programming challenge, you will calculate your age, and your pet’s age from your birthdates, and your pet’s age in dog years. In the code below, type in the current year, the year you were born, the year your dog or cat was born (if you don’t have one, make one up!) in the variables below. Then write formulas in assignment statements to calculate how old you are, how old your dog or cat is, and how old they are in dog years which is 7 times a human year. Finally, print it all out.

Calculate your age and your pet’s age from the birthdates, and then your pet’s age in dog years. If you want an extra challenge, try reading the values using a Scanner.

1.4.8. Summary ¶

Arithmetic expressions include expressions of type int and double.

The arithmetic operators consist of +, -, * , /, and % (modulo for the remainder in division).

An arithmetic operation that uses two int values will evaluate to an int value. With integer division, any decimal part in the result will be thrown away, essentially rounding down the answer to a whole number.

An arithmetic operation that uses at least one double value will evaluate to a double value.

Operators can be used to construct compound expressions.

During evaluation, operands are associated with operators according to operator precedence to determine how they are grouped. (*, /, % have precedence over + and -, unless parentheses are used to group those.)

An attempt to divide an integer by zero will result in an ArithmeticException to occur.

The assignment operator (=) allows a program to initialize or change the value stored in a variable. The value of the expression on the right is stored in the variable on the left.

During execution, expressions are evaluated to produce a single value.

The value of an expression has a type based on the evaluation of the expression.

Java Compound Operators

Last updated: March 17, 2024

• Java Operators

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1. Overview

In this tutorial, we’ll have a look at Java compound operators, their types and how Java evaluates them.

We’ll also explain how implicit casting works.

2. Compound Assignment Operators

An assignment operator is a binary operator that assigns the result of the right-hand side to the variable on the left-hand side. The simplest is the “=” assignment operator:

This statement declares a new variable x , assigns x the value of 5 and returns 5 .

Compound Assignment Operators are a shorter way to apply an arithmetic or bitwise operation and to assign the value of the operation to the variable on the left-hand side.

For example, the following two multiplication statements are equivalent, meaning  a and b will have the same value:

It’s important to note that the variable on the left-hand of a compound assignment operator must be already declared. In other words,  compound operators can’t be used to declare a new variable.

Like the “=” assignment operator, compound operators return the assigned result of the expression:

Both x and y will hold the value 3 .

The assignment (x+=2) does two things: first, it adds 2 to the value of the variable x , which becomes  3;  second, it returns the value of the assignment, which is also 3 .

3. Types of Compound Assignment Operators

Java supports 11 compound assignment operators. We can group these into arithmetic and bitwise operators.

Let’s go through the arithmetic operators and the operations they perform:

• Incrementation: +=
• Decrementation: -=
• Multiplication: *=
• Division: /=
• Modulus: %=

Then, we also have the bitwise operators:

• AND, binary: &=
• Exclusive OR, binary: ^=
• Inclusive OR, binary: |=
• Left Shift, binary: <<=
• Right Shift, binary: >>=
• Shift right zero fill: >>>=

Let’s have a look at a few examples of these operations:

As we can see here, the syntax to use these operators is consistent.

4. Evaluation of Compound Assignment Operations

There are two ways Java evaluates the compound operations.

First, when the left-hand operand is not an array, then Java will, in order:

• Verify the operand is a declared variable
• Save the value of the left-hand operand
• Evaluate the right-hand operand
• Perform the binary operation as indicated by the compound operator
• Convert the result of the binary operation to the type of the left-hand variable (implicit casting)
• Assign the converted result to the left-hand variable

Next, when the left-hand operand is an array, the steps to follow are a bit different:

• Verify the array expression on the left-hand side and throw a NullPointerException  or  ArrayIndexOutOfBoundsException if it’s incorrect
• Save the array element in the index
• Check if the array component selected is a primitive type or reference type and then continue with the same steps as the first list, as if the left-hand operand is a variable.

If any step of the evaluation fails, Java doesn’t continue to perform the following steps.

Let’s give some examples related to the evaluation of these operations to an array element:

As we’d expect, this will throw a  NullPointerException .

However, if we assign an initial value to the array:

We would get rid of the NullPointerException, but we’d still get an  ArrayIndexOutOfBoundsException , as the index used is not correct.

If we fix that, the operation will be completed successfully:

Finally, the x variable will be 6 at the end of the assignment.

5. Implicit Casting

One of the reasons compound operators are useful is that not only they provide a shorter way for operations, but also implicitly cast variables.

Formally, a compound assignment expression of the form:

is equivalent to:

E1 – (T)(E1 op E2)

where T is the type of E1 .

Let’s consider the following example:

Let’s review why the last line won’t compile.

Java automatically promotes smaller data types to larger data ones, when they are together in an operation, but will throw an error when trying to convert from larger to smaller types .

So, first,  i will be promoted to long and then the multiplication will give the result 10L. The long result would be assigned to i , which is an int , and this will throw an error.

This could be fixed with an explicit cast:

Java compound assignment operators are perfect in this case because they do an implicit casting:

This statement works just fine, casting the multiplication result to int and assigning the value to the left-hand side variable, i .

6. Conclusion

In this article, we looked at compound operators in Java, giving some examples and different types of them. We explained how Java evaluates these operations.

Finally, we also reviewed implicit casting, one of the reasons these shorthand operators are useful.

As always, all of the code snippets mentioned in this article can be found in our GitHub repository .

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Class Double

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Field Summary

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Field detail, positive_infinity, negative_infinity, max_exponent, min_exponent, constructor detail, method detail, tohexstring.

FloatValue: Sign opt NaN Sign opt Infinity Sign opt FloatingPointLiteral Sign opt HexFloatingPointLiteral SignedInteger HexFloatingPointLiteral : HexSignificand BinaryExponent FloatTypeSuffix opt HexSignificand: HexNumeral HexNumeral . 0x HexDigits opt . HexDigits 0X HexDigits opt . HexDigits BinaryExponent: BinaryExponentIndicator SignedInteger BinaryExponentIndicator: p P

parseDouble

Doublevalue.

(int)(v^(v>>>32))

long v = Double.doubleToLongBits(this.doubleValue());

d1.doubleValue() == d2.doubleValue()

• If d1 represents +0.0 while d2 represents -0.0 , or vice versa, the equal test has the value false , even though +0.0==-0.0 has the value true . This definition allows hash tables to operate properly. Overrides: equals  in class  Object Parameters: obj - the object to compare with. Returns: true if the objects are the same; false otherwise. See Also: doubleToLongBits(double)

doubleToLongBits

Doubletorawlongbits, longbitstodouble.

int s = ((bits >> 63) == 0) ? 1 : -1; int e = (int)((bits >> 52) & 0x7ffL); long m = (e == 0) ? (bits & 0xfffffffffffffL) << 1 : (bits & 0xfffffffffffffL) | 0x10000000000000L;

• 0.0d is considered by this method to be greater than -0.0d . This ensures that the natural ordering of Double objects imposed by this method is consistent with equals . Specified by: compareTo  in interface  Comparable < Double > Parameters: anotherDouble - the Double to be compared. Returns: the value 0 if anotherDouble is numerically equal to this Double ; a value less than 0 if this Double is numerically less than anotherDouble ; and a value greater than 0 if this Double is numerically greater than anotherDouble . Since: 1.2

Submit a bug or feature For further API reference and developer documentation, see Java SE Documentation . That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples. Copyright © 1993, 2024, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms . Also see the documentation redistribution policy .

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Java Tutorial

Java methods, java classes, java file handling, java how to's, java reference, java examples, java operators.

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

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Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Java divides the operators into the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Bitwise operators

Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations.

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Java Assignment Operators

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :

The addition assignment operator ( += ) adds a value to a variable:

A list of all assignment operators:

Java Comparison Operators

Comparison operators are used to compare two values (or variables). This is important in programming, because it helps us to find answers and make decisions.

The return value of a comparison is either true or false . These values are known as Boolean values , and you will learn more about them in the Booleans and If..Else chapter.

In the following example, we use the greater than operator ( > ) to find out if 5 is greater than 3:

Java Logical Operators

You can also test for true or false values with logical operators.

Logical operators are used to determine the logic between variables or values:

Java Bitwise Operators

Bitwise operators are used to perform binary logic with the bits of an integer or long integer.

Note: The Bitwise examples above use 4-bit unsigned examples, but Java uses 32-bit signed integers and 64-bit signed long integers. Because of this, in Java, ~5 will not return 10. It will return -6. ~00000000000000000000000000000101 will return 11111111111111111111111111111010

In Java, 9 >> 1 will not return 12. It will return 4. 00000000000000000000000000001001 >> 1 will return 00000000000000000000000000000100

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Multiply 10 with 5 , and print the result.

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Java Assignment Shortcuts

• More on Data Types
• Type Conversion and Casting

There are shortcuts in Java that let you type a little less code without introducing any new control structures.

Declaring and Assigning Variables You can declare multiple variables of the same type in one line of code:

You can also assign multiple variables to one value:

This code will set c to 5 and then set b to the value of c and finally a to the value of b .

Changing a variable One of the most common operations in Java is to assign a new value to a variable based on its current value. For example:

Since this is so common, Java let's you shorten it with a combined += operator that lets you skip the variable repetition:

(Note: Do not confuse this with index =+ 1; which would just assign positive 1 to index .)

In fact, any of the arithmetic operators can be used in this way:

j started at 3 and ended up at 5 after the above operations.

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Difference Between Destructuring Assignment and Dot Notation in JavaScript

JavaScript offers various ways to access and assign values from the objects and arrays. Two common methods are destructuring assignment and dot notation. Understanding the differences between these methods can help us write more efficient and readable code.

These are the following topics that we are going to discuss:

Table of Content

What is Destructuring Assignment?

What is dot notation, difference between destructuring assignment and dot notation in javascript.

The Destructuring assignment is a JavaScript feature introduced in the ES6 that allows you to extract values from the arrays or properties from the objects into the distinct variables. This syntax provides a more concise and readable way to unpack values.

Characteristics:

• Concise Syntax: It allows for the shorter and more readable code.
• Pattern Matching: Can extract multiple properties or elements in one statement.
• Default Values: We can assign default values if the unpacked value is undefined.
• Nested Destructuring: It supports extracting properties from the nested objects and arrays.

Applications:

• Simplifying variable assignments.
• Extracting multiple properties from an object at once.
• Using in the function parameters to directly extract properties.

Example: In this example, Object Destructuring extracts ‘name’, ‘age’, and ’email’ from the ‘user’ object and the Array Destructuring extracts the first two elements and collects the rest into an array.

The Dot notation is a straightforward way to access object properties by using the dot followed by the property name. It is the most commonly used method to read and assign properties in JavaScript objects.

• Simplicity: Easy to read and understand.
• Direct Access: Directly access nested properties.
• Property Names: Can only be used with the valid JavaScript identifiers.
• The Accessing and assigning single properties.
• The Navigating through object properties.
• The Simple and straightforward property access.

Example: In this example, Accesses and logs properties of the ‘user’ object, then updates and logs the ‘age’ property.

Both destructuring assignment and dot notation are useful tools in JavaScript for the accessing and assigning values from the objects and arrays. The Destructuring assignment is particularly powerful when dealing with the multiple properties or nested structures offering a concise and readable syntax. Dot notation on the other hand is straightforward and ideal for the accessing single properties. Understanding when and how to the use each can significantly improve the efficiency and readability of the code.

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double colon assignment on method with two parameters

I am using lamdbas so I can consistently set the properties of a ModelObject according to the values I can retrieve from three different objects. The code works like this:

I have read here that it is possible to rewrite bar(value -> model.setB(value), bObject); to bar(model::setB, bObject) . I think this looks better and more concise, but I haven't found a way to rewrite the setA method to a double :: notation. Can anyone tell me if this is possible, and if so: how is this possible?

• 2 Please refer this Method References Link . Shows all kinds of method references. Hope this helps –  Rohit Gulati Commented Jan 17, 2017 at 13:36
• I do not think it is possible. –  toongeorges Commented Jan 17, 2017 at 13:48

4 Answers 4

from https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html and https://www.codementor.io/eh3rrera/tutorials/using-java-8-method-reference-du10866vx

There would be 4 different kinds of method references. The corresponding lambda and method reference:

• (args) -> Class.staticMethod(args), Class::staticMethod
• (obj, args) -> obj.instanceMethod(args), ObjectType::instanceMethod
• (args) -> obj.instanceMethod(args), obj::instanceMethod
• (args) -> new ClassName(args), ClassName::new

The lambda value -> model.setA(CONSTANT, value) does not correspond with any of the lambdas above, so it is not possible to rewrite it as a method reference.

• The reason why I accepted this answer is: while the other answers are clever and useful, they don't make my code more understandable or cleaner. So I'll stick to using the -> notation. –  ivospijker Commented Jan 17, 2017 at 14:06

To use the double colon notation, the method that you're referencing must have the same signature as the required method. So you can't use :: unless you change your IModel :

You can add an overload of setA in IModel :

Then, you can reference that overload:

• To change the IModel would be too much work in order to use a cleaner notation in this case. I hadn't seen the default keyword before, so I'll look into that for the future! –  ivospijker Commented Jan 17, 2017 at 14:00

Not with the way the Setter functional interface is written. Unlike setB and setC , the setA method expects two arguments whereas the interface Setter has a method expecting only one argument. You can add another interface that accepts two arguments:

Then you can call it via the bar method:

Then you can call bar as follows:

Note: You can keep the other bar method. The new one can be an overload.

• But what should be done with the other bar calls that the OP listed without the CONSTANT parameter? –  Sweeper Commented Jan 17, 2017 at 13:47
• 1 @Sweeper He can keep the other bar method. It's simply an overloaded method. –  M A Commented Jan 17, 2017 at 13:48

You don't need a special interface: setB is a Consumer<String> and setA is a BiConsumer<String, String> . You can then adapt a BiConsumer to a Consumer :

Either with a default method in your interface (if setA is always called with a constant, why not ?):

Either using an adapter of BiConsumer to Consumer :

And using it like this:

Note: I used adapt as an example name, but that's a bad name when you mix it with other adapt overload method (because of generic and type erasure). I personally name it like fixLeftValue .

Beware that the adapt will be generated each time you invoke foo .

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