In Java, addition and concatenation are two different operations that involve combining values.

Addition is a mathematical operation that involves adding two or more numerical values together. In Java, addition is performed using the "+" operator. For example, if you have two integer values x and y, you can add them together using the following code:

int result = x + y;

This will add the values of x and y and store the result in the variable "result".

Concatenation, on the other hand, involves combining two or more strings of text. In Java, concatenation is performed using the "+" operator as well, but with strings instead of numbers. For example, if you have two string values str1 and str2, you can concatenate them using the following code: 

String result = str1 + str2;

This will combine the values of str1 and str2 and store the result in the variable "result". Note that when using the "+" operator with strings, the order in which the values are added together matters. For example, if you swap the positions of str1 and str2 in the code above, the resulting string will be different.

In summary, while addition is used to combine numerical values, concatenation is used to combine strings of text in Java.