The Open/Closed Principle calls for adding new code/functionality without modifying the existing code. What is the benefit from doing so?  

What is the output of the code below? Explain the observed behavior in detail. Map a = new HashMap(); Map b = new HashMap(); a.put(“c”, 130); b.put(“c”, 130); System.out.println(a.get(“c”) == b.get(“c”)); // output:

What is the output of the code below? Explain the observed behavior in detail. String s1 = “hello”; String s2 = “hello”; System.out.println( s1 == s2 ); // output:

Why is deep inheritance problematic?

What is the output of the following code?     class A {               void foo() {  System.out.println(“1”); }               public A() {  System.out.println(“2”); foo();    }     }     class B extends A {               public B() { System.out.println(“3”);  }               void foo() { System.out.println(“4”);  }     }      public class Client {               public static void main(String [] args) {                              new B();               }    }

Assuming list is non-empty, does this code compile or not? Explain.   public void func(List list){       list.add(“Hello”);    }

Given two objects a and b such that a.equals(b) is true. Should a.hashCode() and b.hashCode() be also equal? Justify your answer. Yes No Justification:

Given the class hierarchy below. Could the symmetry of equals() be violated? If yes, provide client code that demonstrates that.   class A {   int x;   public A(int x) {this.x = x;}   public boolean equals(Object o) {        if (!(o instanceof A)) return false;        A a = (A)o;        return this.x == a.x;   }        } class B extends A {   int y;   public B(int x, int y) {super(x); this.y = y;}   public boolean equals(Object o) {        if (!(o instanceof B)) return false;        B b = (B)o;        return super.equals(o) && this.y == b.y;   } }                

Does the code below compile? Explain.   public class Utils {      public static void main(String[] args ) throws Exception {                           E e = new E();    } }

What is the output of the code below? Explain. (Note: there are no compilation errors)   class A {                public int x;                public A(int x) { this.x = x; }                public String toString() { return “x = ” + x; } }   class Super {   public A a;   public Super() {                System.out.println(“Super()”);                foo();   }   public Super (A a) {                System.out.println(“Super(A a)”);                this.a = a;                foo();   }   public void foo() {                System.out.println(“Super.foo()”);                System.out.println(a);   } }   public class Sub extends Super {   public A a;   public Sub() {                System.out.println(“Sub()”);                foo();   }   public Sub (A a) {                System.out.println(“Sub(A a)”);                this.a = a;                foo();   }   @Override public void foo() {                    System.out.println(“Sub.foo()”);                System.out.println(a);   } } public static void main(String[] args) { new Super(); }