Mar 05: Memory Diagrams

Learning Objectives

After today's class, you should be able to:

• Describe primitive values and references in a memory diagram.
• Draw memory diagrams that have variables, arrays and objects.
• Summarize differences between variables, arrays, and objects.

Reminders

• Continue reading Week 7
• Make progress on HW 5

On the Board

Memory Diagrams – how to draw pictures like Java Visualizer

Exercise 1: Variables

long money = 50;
boolean good = true;
double price = money;
char hash = '#';
String rating = "PG";

Exercise 2: Arrays

int[] data = null;
int[] counts = {10, 3, 7, -5};
double[] scores = new double[3];
String[] words = new String[2];
String[] take = {"CS 159", "CS 227"};

int[] easy = {1, 2, 3};
int[] copy = easy;

Exercise 3: Methods

public static void main(String[] args) {
    int[] nums = {159, 227};
    printArray(nums);
}

public static void printArray(int[] a) {
    System.out.print("{" + a[0]);
    for (int i = 1; i < a.length; i++) {
        System.out.print(", " + a[i]);
    }
    System.out.println("}");
}

Exercise 4: Objects

public class Card {

    private int rank;  // 1=Ace, ..., 11=Jack, 12=Queen, 13=King
    private int suit;  // 0=Clubs, 1=Diamonds, 2=Hearts, 3=Spades

    public Card(int rank, int suit) {
        this.rank = rank;
        this.suit = suit;
    }

    public static void main(String[] args) {
        Card c1 = new Card(8, 1);
        Card c2 = new Card(12, 2);
        Card c3 = c1;
        c1 = c2;
    }
}

Exercise 5: Static

public class BankAccount {

    private static final String PREFIX = "1234";
    private static int nextNumber = 1;

    private String number;
    private String owner;
    private double balance;

    public BankAccount(String owner) {
        this.number = PREFIX + String.format("%04d", nextNumber);
        this.owner = owner;
        nextNumber++;
    }

    public static void main(String[] args) {
        BankAccount ba1 = new BankAccount("Stacie");
        BankAccount ba2 = new BankAccount("Trevor");
    }
}