The == and != operators are binary operators that evaluate to true or false depending on whether the operands are equal. The == operator gives true if the operands are equal and false otherwise. The != operator gives false if the operands are equal and true otherwise.

These operators can be used operands with primitive and reference types, but the behavior is significantly different. According to the JLS, there are actually three distinct sets of these operators:

• The Boolean == and != operators.
• The Numeric == and != operators.
• The Reference == and != operators.

However, in all cases, the result type of the == and != operators is boolean.

The Numeric == and != operators

When one (or both) of the operands of an == or != operator is a primitive numeric type (byte, short, char, int, long, float or double), the operator is a numeric comparison. The second operand must be either a primitive numeric type, or a boxed numeric type.

The behavior other numeric operators is as follows:

1. If one of the operands is a boxed type, it is unboxed.
2. If either of the operands now a byte, short or char, it is promoted to an int.
3. If the types of the operands are not the same, then the operand with the “smaller” type is promoted to the “larger” type.
4. The comparison is then carried out as follows:

- If the promoted operands are `int` or `long` then the values are tested to see if they are identical.
- If the promoted operands are `float` or `double` then:
  - the two versions of zero (`+0.0` and `-0.0`) are treated as equal
  - a `NaN` value is treated as not equals to anything, and
  - other values are equal if their IEEE 754 representations are identical.

Note: you need to be careful when using == and != to compare floating point values.

The Boolean == and != operators

If both operands are boolean, or one is boolean and the other is Boolean, these operators the Boolean == and != operators. The behavior is as follows:

1. If one of the operands is a Boolean, it is unboxed.
2. The unboxed operands are tested and the boolean result is calculated according to the following truth table

A | B | A == B | A != B | —— | —— | —— | —— | false | false | true | false | false | true | false | true | true | false | false | true | true | true | true | false |