The operators +, -, **, */, and % can be combined with the assignment operator to form augmented operators. Very often the current value of a variable is used, modified, and then reassigned back to the same variable. For example, the following statement increases the variable count by 1:

count = count + 1;

Java allows you to combine assignment and addition operators using an augmented (or compound) assignment operator. For example, the preceding statement can be written as

count += 1;

The += is called the addition assignment operator. More are -=, **=, */=, and **%=.
The augmented assignment operator is performed last after all the other operators in the expression are evaluated. For example,

x /= 4 + 5.5 * 1.5;

is same as

x = x / (4 + 5.5 * 1.5);

There are no spaces in the augmented assignment operators. For example, + = should be +=

Like the assignment operator (=), the operators (+=, -=, **=, */=, **%=) can be used to form an assignment statement as well as an expression. For example, in the following code, x += 2 is a statement in the first line and an expression in the second line.

x += 2; // Statement
System.out.println(x += 2); // Expression