...Problem Set 1

Create an interface to describe a warship in the game "Battleship". The interface should include the following:

method arguments return type

length none int

orientation none 1=North, 2=East, 3=West, 4=South

name none String

take damage int void
Create five implementations of the battleship above.

Consider the following abstract class:

Builder.java
1	public abstract class Builder {
2	// Appends just one character
3	public abstract void append(char c);
4
5	// Force implementer to create a toString method.
6	public abstract String toString();
7
8	// Makes use of the append(char) method
9	// to append a whole string.
10	public void append(String s) {
11	for(int i=0;i<s.length();i++) {
12	append(s.charAt(i));
13	}
14	}
15
16	// Makes use of the fact that all Objects
17	// have a toString() method to format all
18	// other objects.
19	public void append(Object o) {
20	if(o == null)
21	append("null");
22	else
23	append(o.toString());
24	}
25	}
$ javac Builder.java

and the following implementation:

CapBuilder.java
1	public class CapBuilder extends Builder {
2	StringBuffer sb = new StringBuffer();
3	public void append(char c) {
4	sb.append(Character.toUpperCase(c));
5	}
6	public String toString() {
7	return sb.toString();
8	}
9	public static void main(String[] args) {
10	CapBuilder cb = new CapBuilder();
11	cb.append("Hello, world.");
12	System.out.println(cb);
13	}
14	}
$ javac CapBuilder.java
$ java CapBuilder HELLO, WORLD.

We want to create a new Builder, NumBuilder, that converts digits to words, i.e. the string "1, 2, and 3." becomes "One, Two and Three." The string "10" becomes "OneZero". Most of the method is given to you, just fill in the append method. You may not use a loop construct ("for" or "while").

NumBuilder.java
1	public class NumBuilder extends Builder {
2	StringBuffer sb = new StringBuffer();
3	public void append(char c) {
4	// What goes here?
5	}
6	public String toString() {
7	return sb.toString();
8	}
9	public static void main(String[] args) {
10	NumBuilder nb = new NumBuilder();
11	nb.append("1, 2, and 3.");
12	System.out.println(nb);
13	nb.append("4 and 5");
14	}
15	}
$ javac NumBuilder.java

Write a program to find the first 10 prime numbers, i.e. integers that are only evenly divisible by themselves and 1. Hint: Make a big array of booleans named "isprime" and mark off all the non-prime numbers as false, i.e. isprime[4] = false.