teaching machines

CS 145 Lecture 27 – Final review

May 11, 2012 by Chris Johnson. Filed under cs145, lectures, spring 2012.

Agenda

• our own String class
• indexOf
• replace
• startsWith
• concat
• a 2-D ripple
• a bus counter
• Bingo board

Code

MyString.java

package prefinal;

public class MyString {
  private char[] charries;
  
  public MyString(char[] src) {
    charries = src;
  }

  /**
   * Gets the index of first instance of the
   * specified character. If character cannot
   * be found, -1 is returned.
   */
  public int indexOf(char c) {
    for (int i = 0; i < charries.length; ++i) {
      if (charries[i] == c) {
        return i;
      }
    }
    
    return -1; 
  }
  
  public int lastIndexOf(char c) {
    for (int i = charries.length - 1; i >= 0; --i) {
      if (charries[i] == c) {
        return i;
      }
    }
    
    return -1; 
  }
  
  public int length() {
    return charries.length;
  }
  
  public char charAt(int i) {
    return charries[i];
  }
  
  public boolean startsWith(MyString prefix) {
    // This string isn't long enough to even contain prefix.
    // Oh my goodness! Let's get outta here.
    if (prefix.length() > length()) {
      return false;
    }
    
    for (int i = 0; i < prefix.length(); ++i) {
      if (prefix.charAt(i) != charAt(i)) {
        return false;
      }
    }
   
    return true;
  }
  
  public static void main(String[] args) {
    MyString stuff = new MyString("The quick brown fox jumped over the lazy dog".toCharArray());
    System.out.println(stuff.indexOf('T'));
    System.out.println(stuff.indexOf('q'));
    System.out.println(stuff.indexOf('z'));
    System.out.println(stuff.indexOf('3'));
    System.out.println(stuff.lastIndexOf('.'));
    System.out.println(stuff.lastIndexOf('u'));
    System.out.println(stuff.startsWith(new MyString("Bless you".toCharArray())));
    System.out.println(stuff.startsWith(new MyString("".toCharArray())));
  }
}

Ripple.java

package prefinal;

import java.io.FileNotFoundException;
import java.io.PrintWriter;

public class Ripple {
  public static void main(String[] args) throws FileNotFoundException {
    double[][] heights = new double[100][100];
    
    for (int r = 0; r < heights.length; ++r) {
      for (int c = 0; c < heights[r].length; ++c) {
        int diffX = c - heights[r].length / 2;
        int diffY = r - heights.length / 2;
        double distance = Math.sqrt(diffX * diffX + diffY * diffY);
        heights[r][c] = Math.sin(distance);
      }
    }
    
    PrintWriter out = new PrintWriter("/home/user/Desktop/heights.txt");
    for (int r = 0; r < heights.length; ++r) {
      for (int c = 0; c < heights[r].length; ++c) {
        out.print(heights[r][c] + " ");
      }
      out.println();
    }
    out.close();
  }
}

Haiku