Difference between equals() and == in Java

Before discussing the difference between “==” and the equals() method, it’s important to understand that an object has both a location in memory and a specific state depending on the values that are inside the object.

In Java, when the “==” operator is used to compare 2 objects, it checks to see if the objects refer to the same place in memory.

The equals method is defined in the Object class, from which every class is either a direct or indirect descendant.By default equals() will behave the same as the “==” operator and compare object locations. But, when overriding the equals() method, you should compare the values of the object instead.

In Java, == always just compares two references (for non-primitives, that is) - i.e. it tests whether the two operands refer to the same object.

However, the equals method can be overridden - so two distinct objects can still be equal.

For example:

String x = "hello";
String y = new String(new char[] { 'h', 'e', 'l', 'l', 'o' });

System.out.println(x == y); // false
System.out.println(x.equals(y)); // true

Additionally, it's worth being aware that any two equal string constants (primarily string literals, but also combinations of string constants via concatenation) will end up referring to the same string. For example:

String x = "hello";
String y = "he" + "llo";
System.out.println(x == y); // true!

Here x and y are references to the same string, because y is a compile-time constant equal to "hello".