String a = new String("A");
String b = a; //b указывает на "A"
b = "B"; //b указывает новую строку "B"

LJ>public class TestConsole
LJ>{
LJ>  public static void main(String[] args)
LJ>  {    
LJ>    Foo ob = new Foo();
LJ>//в следующей строке получаем указатель на "123"
LJ>    String str = ob.getString();
LJ>    System.out.println(ob.getString());
LJ>//здесь мы меняем указатель внешней переменной - создаем новый String объект! при этом ob.m_Str указывает на старый объект.
LJ>    str = "321";
LJ>    System.out.println(ob.getString());
LJ>  }   
LJ>}
LJ>

String a, b;
a = "hello";
b = "hello";
System.out.println(a == b);

    String s1 = "123";
    String s2 = "123";
    String s3 = new String("123");
    System.out.println(s1 == s2);
    System.out.println(s1 == s3);

String str1 = "bla";
String str2 = "bla";

String str1 = "bla";
String str2 = new String(str1);

   /**
     * Initializes a newly created <code>String</code> object so that it
     * represents the same sequence of characters as the argument; in other
     * words, the newly created string is a copy of the argument string. Unless 
     * an explicit copy of <code>original</code> is needed, use of this 
     * constructor is unnecessary since Strings are immutable. 
     *
     * @param   original   a <code>String</code>.
     */
    public String(String original) {
     this.count = original.count;
     if (original.value.length > this.count) {
         // The array representing the String is bigger than the new
         // String itself.  Perhaps this constructor is being called
         // in order to trim the baggage, so make a copy of the array.
         this.value = new char[this.count];
         System.arraycopy(original.value, original.offset,
                  this.value, 0, this.count);
     } else {
         // The array representing the String is the same
          // size as the String, so no point in making a copy.
         this.value = original.value;
     }
    }

public class TestConsole
{
  public static void main(String[] args)
  {    
    Foo ob = new Foo();
    String str = ob.getString();    
    System.out.println(ob.getString());
    str = "321";
    System.out.println(ob.getString());
  }   
}

class Foo
{
  public String getString()
  {
    return m_Str;
  }
  
  private String m_Str = "123";
}

123
123

private String m_Str = "123"; //Так
private String m_Str = new String("123"); //И так

T>public void doSome(String str){
T> str+="456";
T>}

str+="456";

str = new StringBuilder().append(str).append("456").toString();