Copying one object to another Object is yielding different results in java

Question

public static void main(String[] args) {
    Integer a = 1;
    Integer b = 0;
    b=a;
    System.out.println(a);
    System.out.println(b);
    ++a;
    System.out.println(a);
    System.out.println(b);
}

output : 1 1 2 1

public static void main(String[] args) {
    ArrayList<Integer> a = new ArrayList<Integer>();
    ArrayList<Integer> b = new ArrayList<Integer>();
    a.add(1);
    a.add(1);
    a.add(1);
    a.add(1);
    b=a;
    System.out.println(a.size());
    System.out.println(b.size());
    b.add(2);
    System.out.println(a.size());
    System.out.println(b.size());
}

output : 4 4 5 5

For above code why both objects are not referring to same memory location.

Answer 1

All the wrapper classes are immutable in Java actually. We know String as a famous immutable class. In addition to it other wrappers like Integer is also immutable.

See this http://www.javaworld.com/article/2077343/learn-java/java-s-primitive-wrappers-are-written-in-stone.html