teaching machines

CS 145 Lecture 29 – ArrayList and the So Far Pattern

November 10, 2014 by Chris Johnson. Filed under cs145, fall 2014, lectures.

Agenda

• what ?s
• what does this do?
• arrays as collections
• the so-far pattern

What Does This Do?

• ArrayList people = new ArrayList();
• Random g = new Random();
•  people.add(g.nextPerson());
•  people.add(g.nextPerson());
•  people.add(g.nextPerson());
•  people.add(g.nextPerson());
•  people.add(g.nextPerson());
• System.out.println(people.size());
• System.out.println(people.get(1).getName());
• people.get(4).jump(3);
• people.get(0).highFive(people.get(3));
• people.add(people.get(2));
• people.remove(2);

• int sum = 0;
  for (int i = 0; i < people.size(); ++i) {
    sum += people.get(i).getSiblings().size();
  }
  System.out.println(sum);

• Person winner = people.get(0);
  for (int i = 1; i < people.size(); ++i) {
    if (people.get(i).getDateOfBirth().isBefore(winner.getDateOfBirth())) {
      winner = people.get(i);
    }
  }
  System.out.println(winner.getName());

• Person tmp = people.get(2);
  people.set(2, people.get(1));
  people.set(1, tmp);

• for (int i = 0; i < people.size(); ++i) {
    for (int j = 0; j < people.size(); ++j) {
      if (i != j) {
        people.get(i).shakeHands(people.get(j));
      }
    }
  }

• people.clear();

For-each/Map

make new array same size as old
for each element in old
  transform element
  drop it in the corresponding location in the new array

So Far/Fold/Reduce

initialize so-far
for each element in array
  combine element with so-far

Code

Sort.java

package lecture1110;

import java.util.Arrays;

public class Sort {
  public static void main(String[] args) {
    double[] times = {22.183333, 22.25, 21.6, 21.883333, 22.2, 22.5, 17.616667, 21.4, 20.716667, 22.166667, 21.233333, 21.183333, 18.85, 19.85, 22.1, 20.533333, 21.566667, 22.466667, 20.95, 22.033333, 21.7, 20.516667, 21.35, 21.233333, 21.233333, 21.466667, 21.066667, 21.416667, 19.483333, 20.016667, 21.016667, 20.25, 22.433333, 20.133333, 20.516667, 22.483333, 22.466667, 18.466667, 16.783333, 21.433333, 20.7, 22.516667, 22.4, 19.466667, 21.466667, 17.233333, 20.933333, 22.35, 20.216667, 19.55, 16.9, 18.333333, 20.633333, 21.016667, 20.6, 21.466667, 18.5, 22.383333, 21.566667, 22.483333, 21.433333, 21.433333, 21.683333, 20.783333, 22.433333, 20.85, 22.533333, 20.0, 21.45, 21.816667, 17.516667, 21.033333, 20.05, 22.066667, 18.366667, 20.816667, 21.5, 22.016667, 19.633333, 21.933333, 21.35, 21.716667, 20.216667, 18.35, 21.916667, 21.433333, 22.35, 18.95, 18.55, 21.15, 18.183333, 19.6, 20.833333, 21.05, 21.466667, 21.05, 21.866667, 21.616667, 16.533333, 21.366667};
    Arrays.sort(times);
    
    System.out.println(Arrays.toString(times));
  }
}

Deck.java

package lecture1110;

import java.util.ArrayList;
import java.util.Collections;

public class Deck {
  public static void main(String[] args) {
    String[] suits = {"\u2665", "\u2666", "\u2660", "\u2663"};
    String[] ranks = {"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"};
    
    ArrayList<String> deck = new ArrayList<String>();
    for (String suit : suits) {
      for (String rank : ranks) {
        deck.add(rank + suit);
      }
    }
    Collections.shuffle(deck);
    System.out.println(deck);
      
//    for (int i = 0; i < suits.length; ++i) {
//      String suit = suits[i];
      
  }
}

SoFar.java

package lecture1110;

public class SoFar {
  public static void main(String[] args) {
    int[] numbers = {4, 8, 15, 16, 42, 5, 312, 2000000000};
    System.out.println(sum(numbers));
    System.out.println(max(numbers));
  }
  
  public static int sum(int[] numbers) {
    int sumSoFar = 0;
    for (int number : numbers) {
      sumSoFar += number;
    }
    return sumSoFar;
  }
  
  public static int max(int[] numbers) {
    int maxSoFar = numbers[0];
    for (int i = 1; i < numbers.length; ++i) {
      if (maxSoFar < numbers[i]) {
        maxSoFar = numbers[i];
      }
    }
    return maxSoFar;
  }
}

Haiku