Final exam review

Final exam review:

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"Immutable"
How to make a class immutable?
What is a sample class?

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Override vs. Overload?

Consider the following program. Which overrides which? Which overloads which?

public class A {
 public void f() {
   System.out.println("1");
 }

 public void g(int x) {
   System.out.println("2");
 }
}

public class B extends A {
 private void f() {
   System.out.println("3");
   super.f();
 }

 public void f(int x) {
   System.out.println("4");
 }

 public void g() {
   System.out.println("5");
 }

 // can we have this method?
 private void g(int x) {
   System.out.println("6");
 }
}

Consider the following calls. Which method is called at each line? Which line is an error?

A a = new A();
B b = new B();
a.f(5);
b.f();
b.g(2);
((A)b).f();
A.f();

Answers:
a.f(5); => not compiled
b.f(); => 3, 1
b.g(2); => 2
((A)b).f(); => 1
A.f(); => not compiled

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What is "this"?

public class C {
 private void f() {
   if (this.equals(null)) {
     System.out.println("Duh?");
   }
 }

 public static void main(String args) {
   f();
   OR this.f();
   OR (new C).f();
 }

}
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interface vs abstract class
What are the differences?
When to use which?
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