Difference between string object and string literal
This question already has an answer here:
When you use a string literal the string can be interned, but when you use new String("...") you get a new string object.
In this example both string literals refer the same object:
String a = "abc";
String b = "abc";
System.out.println(a == b); // true
Here, 2 different objects are created and they have different references:
String c = new String("abc");
String d = new String("abc");
System.out.println(c == d); // false
In general, you should use the string literal notation when possible. It is easier to read and it gives the compiler a chance to optimize your code.
A String literal is a Java language concept. This is a String literal:
"a String literal"
A String object is an individual instance of the java.lang.String class.
String s1 = "abcde";
String s2 = new String("abcde");
String s3 = "abcde";
All are valid, but have a slight difference. s1 will refer to an interned String object. This means, that the character sequence "abcde" will be stored at a central place, and whenever the same literal "abcde" is used again, the JVM will not create a new String object but use the reference of the cached String.
s2 is guranteed to be a new String object, so in this case we have:
s1 == s2 // is false
s1 == s3 // is true
s1.equals(s2) // is true
The long answer is available here, so I'll give you the short one.
When you do this:
String str = "abc";
You are calling the intern() method on String. This method references an internal pool of String objects. If the String you called intern() on already resides in the pool, then a reference to that String is assigned to str . If not, then the new String is placed in the pool, and a reference to it is then assigned to str .
Given the following code:
String str = "abc";
String str2 = "abc";
boolean identity = str == str2;
When you check for object identity by doing == (you are literally asking: do these two references point to the same object?), you get true .
However, you don't need to intern() Strings . You can force the creation on a new Object on the Heap by doing this:
String str = new String("abc");
String str2 = new String("abc");
boolean identity = str == str2;
In this instance, str and str2 are references to different Objects , neither of which have been interned, so that when you test for Object identity using == , you will get false .
In terms of good coding practice: do not use == to check for String equality, use .equals() instead.
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