what dose this Sign mean in Java Sign +=

Answer 1

I'll give you an example:
X += Y
is basically same as:
X =X+Y

It is a shortcut to add two values.

Answer 2

it is addition assignment operator...
in which we can add a variable to the given variable and assign it to the same variable...
x+=y
is. equivalent to
x=x+y

Answer 3

https://www.sololearn.com/learn/Java/2141/