What does += mean in Java with examples

In this post, I will be sharing what does += mean in Java with examples. += is known as an addition assignment operator in Java. Addition and assignment can be performed in one step with the help of this operator.

Read Also: String Concatenation in Java

It is also known as a compound assignment operator.

What does += mean in Java with examples

There are many ways in which we can use += in Java.

1. Incrementing int values with += operator

The below code will increase the value of x by 5.

 int x = 10;
x += 5;
System.out.println(x); // Print 15

On the other hand, if we use x++ in the code, it will increment the value of x by 1 as shown below in the example.

 int x = 15;
x++;
System.out.println(x); // Print 16

2. Using += operator in for loop

You can also use the += operator(addition assignment operator) in Java to increment the value of the variable by more than 1.

For example, in the below for loop, we are printing the even numbers from 0 to 15 using the += operator. The value of variable i is incremented by 2 at each iteration of the for loop.

 public class PrintEvenNumber 
{
    public static void main(String args[]) 
    {
        for (int i=0; i < 15; i+=2)
        {
            System.out.print(" "+ i + " ");
        }
    }
}

Output:
0 2 4 6 8 10 12 14

3. Multiple Data types

Data types of two operands determine the behavior of this operator. For example, if the data type of both operands is a number then += will be used for addition. On the other hand, if the datatype of both operands is String then it is used for concatenation.

a. Difference between a=a+b and a+=b in Java

Things get interesting when we have a and b of different data types.

1. Data type of variable a as int and b as double

If we add an int to double using the regular addition expression, we will get an error as shown below in the example:

 public class AdditionAssignmentOperator 
{
    public static void main(String args[]) 
    {
       int x =1;
       x += 2.2; // Print 3, will cast 2.2 to 2 internally
       x = x + 2.2; // Throws compile time error, can not convert from double to int 
       System.out.println(x);
    }
}

Output:
/AdditionAssignmentOperator.java:7: error: incompatible types: possible lossy conversion from double to int
      x = x + 2.2; // Throws compile time error, can not convert from double to int
               ^
1 error

 💡 Did You Know?

According to Oracle docs, a compound statement expression of the form x op= y is equivalent to x = (T) ((x) op (y)) where T is of type x, except that x is evaluated only once.

Let's understand the above line with the help of an example:

The following code is correct:

 int a = 13;
a += 7.03;

The above code will result in a value of 20 because it is equivalent to

 int a = 13;
a = (int) (13 + 7.03);

4. += for String Concatenation

You can use the += addition assignment operator for String concatenation as well, as shown below in the example:

 public class AdditionAssignmentOperator2
{
    public static void main(String args[]) 
    {
       String x = "Alive is";
       x += "Awesome";
       System.out.println(x);
    }
}

Output:
Alive is Awesome

That's all for today. Please mention in the comments if you have any questions related to what does += mean in Java with examples.