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Quiz - 2

This quiz tests your knowledge of Java language semantics. Get a print out of this when you come to the class.

  • First try answering without running the program.
  • Then run the program to check if your understanding was indeed correct.
  • Enter both the answers in the last column and submit.
Concept Program Your answer first, followed by the actual answer
Dynamic
dispatch/
Method
overloading/
Runtime
Polymorphism		 
// NTest.java
public class NTest {
  public static void main(String[] args) {
    NTest nt = new NTest();
    nt.method(2);
    nt.method('2');
  }

  public void method(int i) { // Does nothing }
  public void method(char c) { // Does nothing }
}
Dynamic
dispatch/
method
overloading		 
// OTest.java
public class OTest {
  public static void main(String[] args) {
    OTest ot = new OTest();
    ot.method(2);
    ot.method(2);
  }

  public char method(int a) { return 'c'; }
  public long method(int b) { return 0; }
  /* Is it possible to overload methods that
     differ only on the return type? */
}
Instance
method
accessing
static
variable
& calling
static
method		 
// PTest.java
public class PTest {
  static int var;
  public static void main(String[] args) {
    PTest pt = new PTest();
    pt.instanceMethod();
  }

  public void instanceMethod() {
    var = 0;
    staticMethod();
    /* Is it appropriate to use this.var
       or this.staticMethod()? */
  }

  public static void staticMethod() {
    System.out.println("static method";)
  }
}
Static
method
accessing
instance
variable
& calling
instance
method		 
// QTest.java
public class QTest {
  private int var;
  public static void main(String[] args) {
    var = 0;
    instanceMethod();
  }

  public void instanceMethod() {
    System.out.println("instance method");
  }
}
Working
with null
object		 
// R.java
public class R {
	private int x;
	public void set(int xi) { x = xi; }
}

// RTest.java
public class RTest {
  public static void main(String[] args) {
    R r;
    r.set(2);
  }
}
Working
with null
array		 
// S.java
public class S {
	private int x;
	public void set(int xi) { x = xi; }
}

// STest.java
public class STest {
  public static void main(String[] args) {
    S[] s;
    s.length;
  }
}
Working
with null
array
element		 
// T.java
public class T {
	private int x;
	public void set(int xi) { x = xi; }
}

// TTest.java
public class TTest {
  public static void main(String[] args) {
    T[] t = new T[10];
    t[5].set(2);
  }
}
Crossing
array
boundary		 
// U.java
public class U {
	private int x;
	public void set(int xi) { x = xi; }
	public int get() { return x; }
}

// UTest.java
public class UTest {
  public static void main(String[] args) {
    U[] u = new U[10];
    for (int i=0; i<u.length; i++)
      u.set(i);
    System.out.println( u[10].get() );
  }
}
Default
Constructor		 
// V.java
public class V {
	private int x;
	public V(int xi) { x = xi; }
}

// VTest.java
public class VTest {
  public static void main(String[] args) {
    V v1 = new V(5);
    V v2 = new V();
  }
}
Private
constructor		 
// W.java
public class W {
	private int x;
	private W() { x = 0; }
}

// WTest.java
public class WTest {
  public static void main(String[] args) {
    W w = new W();
  }
}
Empty .java
filename		 
// .java
class X {	// Don't make it public
	private int x;
	public X(int xi) { x = xi; }
}
/* Compilation: javac .java
   Does it compile? Check it out. */
Static block
with main		 
// YTest.java
public class YTest {
  static{
	System.out.println("From static block");
  }
	
  public static void main(String args[]){
    System.out.println("Hello main");
  }
}
Static block
without main		 
// ZTest.java
public class ZTest {
  static{
	System.out.println("From static block");
	System.exit(0);
  }
}