What is += Addition Assignment Operator in Java?

It’s the Addition assignment operator. Let’s understand the += operator in Java and learn to use it for our day to day programming.

x += y in Java is the same as x = x + y.

It is a compound assignment operator. Most commonly used for incrementing the value of a variable since x++ only increments the value by one.

Incrementing Values With the += Operator

This code will increase the value of a by 2. Let’s see the examples:

int a = 1;
a+=2;
System.out.println(a);

On the other hand if we use a++:

int a = 1;
a++;
System.out.println(a);

The value of a is increased by just 1.

Using += in Java Loops

The += operator can also be used with for loop:

for(int i=0;i<10;i+=2)
{
    System.out.println(i);
}

The value of i is incremented by 2 at each iteration.

Working with multiple data types

Another interesting thing to note is that adding int to double using the regular addition expression would give an error in Java.

int a = 1;
a = a + 1.1; // Gives error 
a += 1.1;
System.out.println(a);

The first line here gives an error as int can’t be added to a double.

Output:

error: incompatible types: possible lossy conversion from double to int
a = a + 1.1; // Gives error 

However, when using the += operator in Java, the addition works fine as Java now converts the double to an integer value and adds it as 1. Here’s the output when the code is run with only the += operator addition.

E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once. This is Java doing typecasting to add the two numbers.

String Concatenation

The += operator also works for string mutation.

String a = "Hello";
a+="World";
System.out.println(a);

The string “Hello” has been mutated and the string “World” has been concatenated to it.

Conclusion

The += is an important assignment operator. It is most commonly used with loops. The same assignment also works with other operators like -=, *=, /=.