String Object equality with == operator

[kumar080780]

String str ="Arun"+"Kumar";
String str1="Arun"+"Kumar";
String c = str+str1
String d= str+str1;

According to String Immutability in nature, i have tested for (str==str1) it gives true, but at the same time if i test for (c==d) it gives false why is it so? can any one explain me about this.

[emceenugget]

I believe that str and str1 are referring to the same string in the string constant pool. However, c and d are initialized as string objects of two strings concatenated together.

This may not be correct, so perhaps someone else with more knowledge about this can shed some light?

[J-Live]

boolean equals(Object anObject) Returns true if and only if the argument is a String object that represents the same sequence of characters as this object.
boolean equalsIgnoreCase(String anotherString) Returns true if and only if the argument is a String object that represents the same sequence of characters as this object, ignoring differences in case.

[J-Live]

public class NewClass {
     public static void main(String[] args){
String str ="Arun"+"Kumar";
String str1="Arun"+"Kumar";
String c = str.concat(str1);
String d = str.concat(str1);

if(c.equals(d)){
    System.out.println("C and D are equal. C equals ".concat(c) + ". " + "D equals ".concat(d) + ". ");}
    }
}

[Eranga]

String str ="Arun"+"Kumar";
String str1="Arun"+"Kumar";
String c = str+str1
String d= str+str1;

According to String Immutability in nature, i have tested for (str==str1) it gives true, but at the same time if i test for (c==d) it gives false why is it so? can any one explain me about this.

There is no major relation with immutable and the == operator.

Once you define a string, VM check on string constant pool, and if it's found make a reference to it. So str and str1 refer the same and == return true. Once you concatenating strings and assign to another string object it want happen, VM keep to reference to that, and == operator return false.

Read more about == and equals() on Java docs.