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String Class(Since JDK 1.0)

A String can be constructed by either:

directly assigning a string literal to a String reference - just like a primitive, or
via the "new" operator and constructor, similar to any other classes.However, this is not commonly-used and is not recommended.

String str1="Java is Open";                    
/* implicit Construction via String Literals */
String str2=new String("Java is Easy");     
/* Explicit Construction via new */

Example:

class Test
{
   public static void main(String args[])
   {
/* Initialize String Literals with String Literals value */
     String s1="StringLiterals";
     String s2="StringLiterals";
/* Assign s3 with the value of s2 */
     String s3=s1;
/* Make two String Object with String Object value */
     String s4=new String("StringObject");
     String s5=new String("StringObject");
    }
}

Memory Layout of String Literals and String Object:

Optimization of String Memory Allocation:

The String Literals (Which have same value) can store in String Pool thus the String Objects are store in Heap.
first type of creation is much more faster, Why?
The "new" key word creates new objects for s4 and s5 which is expensive.
Java maintains an internal list of references for interned Strings pool of unique Strings to avoid duplicate String objects in heap memory.
When we making an String Object then the one copy of that String store in String Pool and another in Heap.
String Pool is mainly situated in PermGen (Permanent Generation).
PermGen never be Garbage Collected even JVM executes its Full GC.
It Means String Class make large Garbage.

String Class(Since JDK 1.0)

A String can be constructed by either:

Example:

Memory Layout of String Literals and String Object:

Optimization of String Memory Allocation:

Tutorials Available