What is Concatenation in JAVA?

Concatenation describes the operation of joining two strings together. In Java, the operator "+" normally acts as an arithmetic operator unless one of its operands is a String. If necessary it converts the other operand to a String before joining the second operand to the end of the first operand.

when a + is used for concatenation below are the steps which are involved:

1. A StringBuffer object is created
2. string1 is copied to the newly created StringBuffer object
3. The “*” is appended to the StringBuffer (concatenation)
4. The result is converted to back to a String object.
5. The string1 reference is made to point at that new String.
6. The old String that string1 previously referenced is then made null.

Example:
To join the two Strings "pan" and "handle":

 System.out.println("pan" + "handle"); 

If one of the operands is not a String it will be converted:

 int age = 12; 
 System.out.println("My age is " + age); 

There is also a method called concat defined in the String class that performs the same operation:

 System.out.println("pan".concat("handle"));