CS51 - Fall 2009 - Lecture 39

Given the class definitions below:
public class A{
   public void method1(){
   ...
   }
}
public class B extends A{
   public void method1(String a){
   ...
   }

   public void method2(){
   ...
   }
}
public class C extends B{
   public void method1(){
   ...
   }
}

private A someA;
private B someB;
private C someC;

- what assignments are legal?
- Is someC.method2() a legal call?
- Which classes method1 is called for:
---- someB.method1();
---- someC.method1("this is a string");

What would the call mystery(5) return?
public String mystery(int num){
   if( num <= 1 ){
      return "1";
   }else{
      String returnMe = "";

      for( int i = 0; i < num; i++ ){
         returnMe += num
      }

      return returnMe + mystery(num-1);
   }
}

What does the following method return with the input: [1, 2, 3, 4, 5, 6, 7, 8]?

// length of a is assumed to be even
public int mystery(int[] a){
   int returnVal = 0;

   for( int i = 0; i < a.length/2; i++ ){
      returnVal += a[i] * a[a.length-i-1];
   }

   return returnVal;
}

what does the method below do?

public int[] mystery(int[][] a){
   int[] returnMe = new int[a.length];

   for( int i = 0; i < a.length; i++ ){
      int s = 0;

      for( int j = 0; j < a[i].length; j++ ){
         s += a[i][j];
      }

      if( s > 100 ){
         returnMe[i] = s;
      }else{
         returnMe[i] = 0;
      }
   }

   return returnMe;
}

Why should you use the StringBuffer class?

One of the methods below will not compile. Indicate which one and explain why.

public void methodA(){
   ...
   throw new IOException();
}

public void methodB(){
   ...
   throw new NumberFormatException();
}