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CSE143 Inheritance Examples handout #27
We developed the following class in lecture on Monday:
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);
}
public void translate(int dx, int dy) {
count++;
super.translate(dx, dy);
}
public int getTranslateCount() {
return count;
}
}
It is a variation of the Point class that keeps track of how many times it has
been translated. Below is a sample inheritance question.
1. Programming with inheritance. A cash processing company has developed a
Java class called Account that can be used to process transactions. It has
many methods including the following:
public Account(Client c)
// the only constructor for an Account, takes as a parameter a
// a reference to a Client object that stores start-up information
public boolean process(Transaction t)
// processes the next transaction, returning true if the transaction
// was approved and returning false otherwise
The Transaction class also has many methods including:
public int value()
// returns the value of this transaction in pennies (could be
// negative, positive or zero)
Assume that all transactions enter the system by a call on the process
method described above. The company wishes to create a slight modification
to the Account class that filters out zero-valued transactions. You are to
design a new class called FilteredAccount whose instances can be used in
place of an Account object but which include the extra behavior of not
processing transactions with a value of 0. More specifically, the new class
should indicate that a zero-valued transaction was approved but shouldn't
call the process method in the Account class to process it. Your class
should have a single constructor that takes a parameter of type Client and
it should include the following method:
public double percentFiltered()
// returns the percent of transactions filtered out (between 0.0 and
// 100.0); returns 0.0 if no transactions of any kind have been
// submitted
Write your definition of class FilteredAccount below.
One possible solution appears below.
public class FilteredAccount extends Account {
private int zeros;
private int transactions;
public FilteredAccount(Client c) {
super(c);
zeros = 0;
transactions = 0;
}
public boolean process(Transaction t) {
transactions++;
if (t.value() == 0) {
zeros++;
return true;
} else
return super.process(t);
}
public double percentFiltered() {
if (transactions == 0)
return 0.0;
else
return zeros * 100.0/transactions;
}
}
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