Java String Literals Versus String Objects

Strings in Java can be declared either literally-

String s = "123";

or as a String instance-

String s = new String("123");

What are the differences between these two strings?

package drills;

public class Tester {

  public static void main(String[] args) {

    // Test differences between String v = new String(...)
    // and String v = "..."

    // String literals are stored in a string pool- cached and reused.
    // String objects are stored in the heap as new objects.        

    // Two string literals with the same characters are the same
    // in every possible way.
    String s1 = "abcdef";
    String s2 = "abcdef";
    assert(s1 == s2);
    assert(s1.hashCode() == s2.hashCode());
    assert(s1.equals(s2) && s2.equals(s1));

    // Two string objects with the same characters are the same
    // only with hashCode() and equals()- but are different object
    // instances
    String s3 = new String("abcdef");
    String s4 = new String("abcdef");
    assert(s3 != s4);
    assert(s3.hashCode() == s4.hashCode());
    assert(s3.equals(s4) && s4.equals(s3));

    // String literals and String objects are separate string
    // instances, but hashCodes are all equal
    assert(s1 != s3 && s1 != s4);
    assert(s1.hashCode() == s2.hashCode());
    assert(s2.hashCode() == s3.hashCode());
    assert(s3.hashCode() == s4.hashCode());

    // Though separate instances, contents are also still equal
    assert(s1.equals(s3) && s1.equals(s4));
    assert(s2.equals(s3) && s2.equals(s4));

    System.out.println("Tests completed");
  }
}

Summary:

• Regardless of how strings are declared, for a given character sequence, their hashCodes() and equals() all return the same value.
  • String literals reuse the same string instance if already exists.
  • String objects always create a new instance (unless using the intern method).