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Ace the AP Computer Science Exam for High Schoolers

Assignment Operators

Explore how to assign and update values in Java using assignment operators. Understand the use of compound assignments like += and -=, along with increment ++ and decrement -- operators to manipulate variables efficiently in coding.

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Introduction

We have already seen the assignment operator, which is used to assign a value to a variable or update its value. The “equal to” sign(=) is used for this operator. Anything on the right of = is assigned to the variable on its left.

Therefore, you always need to place a variable on the left side of =, whereas on the right side can be a value or another variable. Another thing you need to be careful about is the type. You can assign a double value or another double type variable only to a double type variable.

Let’s look at some use cases of the assignment operator.

Java
class AssignmentOperator 
{
    public static void main(String args[]) 
    {
        // assignment operator used to assign a value of zero to the newly declared variable
        int var1 = 0;
        System.out.println(var1); // prints the value of var1, i.e., 0
        int var2; // another int type variable declared
        // assignment operator used to assign a value to a previously declared variable
        var2 = 7; 
        System.out.println(var2); // prints value of var2, i.e., 7
      
        // assignment operator used to update the value of var1 to the value of var2
        var1 = var2;
        System.out.println(var1); // prints updated value of var1 i.e. 7
        System.out.println(var2); // value of var2 remains 7
    }
}

Notice that we create an int variable at line 6 and assign it with 00. Next, we declare another int variable: var2 (at line 9). At line 12, we give var2 a value of 77. Look at line 16.The statement, var1 = var2, changes the value of var1. After this statement, var1 equals 77.

You can also use the assignment operator along with arithmetic operators to update the values of variables. For example, if you want to add 88 to the variable, var1, you could do that as follows:

Java
class AssignmentOperatorArithmetic 
{
    public static void main(String args[]) 
    {
        // var1 declared and assigned a value of 7
        int var1 = 7;
        System.out.println(var1); // prints 7
      
        // adding 8 to var1
        var1 = var1 + 8;
        System.out.println(var1); // prints 15
    }
}

At line 10, we are adding 88 to the old value of var1, and storing the result back to var1. This statement makes var1's value equal 1515.

Compound assignment operators

In the example above, when you add 88 to var1, var1 is repeated twice: once on the left side of =, and once on the right. The same will be the case for any other arithmetic operator, i.e., -, *, / and %.

Well, this is not ideal. Writing a variable’s name twice like this can be infuriating. Thus, we have compound assignment operators. By prepending the arithmetic operator to = operator, we get the corresponding arithmetic operator. Thus, we have:

  • +=: Adds the value given on the right side (or the value of a variable given on the right side) to the variable on the left.

  • -=: Subtracts the value given on the right side (or the value of a variable given on the right side) from the variable on the left.

  • *=: Multiplies the value given on the right side (or the value of a variable given on the right side) with the variable on the left.

  • /=: Divides the variable on the left with the value (or value of a variable) given to the right.

  • %=: Takes the module of the variable on the left with the value (or value of a variable) given to the right.

Let’s look at all of these operators in practice in the code below.