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CSE143 Inheritance Examples handout #33
Class StutterList.java
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// Variation of ArrayList that adds values twice with the appending add.
import java.util.*;
public class StutterList<E> extends ArrayList<E> {
public boolean add(E value) {
super.add(value);
super.add(value);
return true;
}
}
Class MyPoint.java
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// Variation of Point that keeps track of how many times each point has been
// translated and that provides a getTranslateCount method.
import java.awt.*;
public class MyPoint extends Point {
private int count;
public MyPoint() {
this(0, 0);
}
public MyPoint(int x, int y) {
super(x, y);
count = 0;
}
public void translate(int dx, int dy) {
count++;
super.translate(dx, dy);
}
public int getTranslateCount() {
return count;
}
}
Class PointTest.java
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// Class that demonstrates simple use of the MyPoint class.
public class PointTest {
public static void main(String[] args) {
MyPoint p = new MyPoint(13, 42);
p.translate(3, 14);
p.translate(72, 4);
p.translate(-8, 9);
System.out.println("Translate count = " + p.getTranslateCount());
}
}
Output of PointTest
-------------------
Translate count = 3
Class UndoStack.java
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// UndoStack is a variation of the Stack class that supports an undo operation
// for reversing the effect of push and pop operations. The canUndo method
// indicates whether an undo is legal.
import java.util.*;
public class UndoStack<E> extends Stack<E> {
private Stack undoStack;
// post: constructs an empty UndoStack
public UndoStack() {
undoStack = new Stack();
}
// post: pushes and returns the given value on top of the stack
public E push(E value) {
super.push(value);
undoStack.push("push");
return value;
}
// post: pops and returns the value at the top of the stack
public E pop() {
E value = super.pop();
undoStack.push(value);
undoStack.push("pop");
return value;
}
// post: returns whether or not an undo can be done
public boolean canUndo() {
return !undoStack.isEmpty();
}
// pre : canUndo() (throws IllegalStateException if not)
// post: undoes the last stack push or pop command
public void undo() {
if (!canUndo()) {
throw new IllegalStateException();
}
if (undoStack.pop().equals("push")) {
super.pop();
} else {
super.push((E) undoStack.pop());
}
}
}
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