Wha is the difference between a = a + b and a += b in Java?

Question

Given 2 strings, a and b, return a string of the form shorterString+longerString+shorterString, with the shorter string on the outside and the longer string on the inside. The strings will not be the same length, but they may be empty (length 0). If input is "hi" and "hello", then output will be "hihellohi".

Answer 1

1 if data type of both a and b are same then no difference.
2 if data type are not same then compiler return error, if not return error means output is not correct;
Ex 1.

int a = 5
float b=1.7;
a += b;
// a == 6  

Ex 2.

byte a = 1;
int b = 2;

a += b; // compiles
a = a + b; // doesn't compile as a byte + int = int
a = (byte) (a + b); // compiles as this is the same as +=

Comments

one thing you missed brother, you have written
a = a + b; // doesn't compile as a byte + int = int (point 2 in your ans) but
this is not true always example:
if you interchange the type like
a = a + b; //  compile as a int=int+byte
so now it is not a lossy conversion and return output successfully.  follow this compiled link :
http://ideone.com/yZSSIz

Answer 2

Hi Anitha the arithmetic expression a+=b is a type of compound assignment operator and according to java language specification,I found that this expression is evaluated as :
"A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once." Example :

     /* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        short a=3;
        double b=3.6;
        System.out.println(a+=b);    // expression is evaluated as a=(short)(a+b); type casting is happening here result is 6
        System.out.println(a=a+b);  //  throws an error : incompatible types: possible lossy conversion from double to short
    }
}

Reference : http://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.26.2

Comments

Thanks for the refference

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welcome