Show description

Figure 2-7. A shallow copy of an object is one that shares with the original object references to the same instances of other referenced objects 46 Chapter 2 ■ Designing Libraries, Classes, and Methods Shallow copies are sometimes acceptable, but not in all cases. For example, when you create a clone of an object, you’ll often do so intending to modify the contents of the clone without changing the original. In that case, a shallow copy may not be sufficient. For example, suppose you’re using the following class: public class MailMessage implements Cloneable { protected String sender; protected String recipient; protected StringBuffer messageText; public MailMessage(String from, String to, String message) { sender = from; recipient = to; messageText = new StringBuffer(message); } public StringBuffer getMessageText() { return messageText; } } If you use clone() to create a duplicate instance of this class, you’ll have a shallow copy that points to the same object instances as the original.

Public int hashCode() { return employeeID; } This would satisfy the first requirement mentioned previously because the value of employeeID would be used to determine equality and would be used as the hash code value. In other words, two instances that have the same employeeID value are considered equal to one another, and they will return the same hash code value. The second requirement is also satisfied, because as long as the employeeID value remains unchanged, the hashCode() method will return the same result each time it’s called.

Both methods add numbers together, and it’s necessary to decide which one should retain that functionality. One of the methods adds two numbers together, and the other adds zero or more numbers together. In other words, the first method provides a 57 Chapter 2 ■ Designing Libraries, Classes, and Methods subset of the functionality of the second one. Since that’s the case, you can eliminate the duplication by delegating responsibility for adding the two numbers to the more flexible method. The following is an alternative implementation: public class AddingMachine { /** * Adds two integers together and returns the result.