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

+1 vote
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Wha is the difference between a = a + b and a += b in Java?
posted Oct 14, 2016 by Anitha

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2 Answers

+1 vote
 
Best answer

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 +=
answer Jan 6, 2017 by Ajay Kumar
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
+3 votes

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

answer Oct 14, 2016 by Shivam Kumar Pandey
Thanks for the refference
welcome
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