What is the difference between the operators += vs =+

+= adds the right operand to left operand and assign it to left operand

=+ assign a value to the left operand

The important fact to highlight is that there is no =+ assignment operator in Java.

You're just listing two operators, one after the other (an = then a +)

• i =+ j; is just like writing i = +j;.

While a little funky looking at it that way, it's very clear to everyone when considering the minus sign.

• i =- j; is the same as i = -j;

As mentioned in many other answers, the Add and Assignment operator +=

• Adds the right hand side expression to the value of the left hand variable
• Then assigns the value of that addition to the left hand variable.

=+ is the same as the assignment operator =

a =+ b;

is equivalent to

a = (+b);

which is the same as

a = b;

A common syntax is:

 +=

This is the add and assignment operator, which adds right-hand expression to the left-hand variable then assigns the result to left-hand variable. For example:

 int i = 1;
 int j = 2;
 i += j;

 // Output: 3
 System.out.println( i )

A far less common syntax is:

=+

Usually this is written as two different operators, separated by a space:

= +

Without the space, it looks as follows:

int i = 1;
int j = 2;
    
i =+ j;

// Output: 2
System.out.println(i);

An idiomatic way to write this is to shift the unary operator to the right-hand side:

int i = 1;
int j = 2;
    
i = +j;

// Output: 2
System.out.println(i);

Now it's easy to see that i is being assigned to the positive value of j. However, + is superfluous, so it's often dropped, resulting in i = j, effectively the equivalent of i = +1 * j. In contrast is the negative unary operator:

int i = 1;
int j = 2;
    
i = -j;

// Output: -2
System.out.println(i);

Here, the - would be necessary because it inverts the signedness of j, effectively the equivalent of i = -1 * j.

See the operators tutorial for more details.