Lecture 9

Special Functions

• already we have seen clone()
• this is a special method that is possessed by all objects
• we will talk about two more in this lecture
• toString()
• equals()

ToString()

• returns an object of type String
  
• 'cast' your object object to a string type
• creates a string output of your objects current state
• contents of all private instance fields
• very useful for debugging
• the compiler uses toString() whenever it needs to cast your object to a String

Example

MyObject x = new MyObject();
System.out.println(x);

• println takes a String argument
• this is equivalent to saying:
• System.out.println(x.toString());

• In a toString method you should do the following
• include the name of the class
• include all the private fields

Example

• if MyObject contains only a private int a
• toString() output should be
• MyObject[a=0]

Equals()

• returns a boolean
  
• true or false
• checks to see whether two objects are equal
• returns true if they are equal, false if they are not

The default form of this method is

Public boolean equals(Object, OtherObject)

• we must use the most general form of the default equals() in order to capture all objects

Public Class MyObject{

private int x;
public boolean equals(Object, OtherObject){
MyObject other = (MyObject)OtherObject;
return (this.x == other.x);

• if x and y are objects and not primitives then
• x==y if x and y point to the same object

Delegation within the class

• Example: code used by many methods in the same class
• Example: Constructors