CSE Lecture 18/Jan/2007

The this Keyword

-this refers to the current object
-this is always legal to use, sometimes makes the program easier to read
-can be used to resolve ambiguities in variable scope.

public class MyClass
{
private int x;
.
.
.
public void printX()
{
System.out.println(x); <--- can replace x by this.x
}
public void printOtherX(MyClass m)
{
System.out.println(this.x);
System.out.println(m.x);
}
}

Note: methods in classes have access to all private members of any object of that same class type(just not this).

This() as a method refers to the constructor of the current object.

public class MyClass
{
private int x;

public MyClass(int x)
{ this.x = x}

public MyClass() //default constructor
{this(0);
}

Two Special Methods: equals() and toString()

toString()

-creates a string representation of your object.
-method is called whenever your object is cast to a String

e.g. MyClass m = new MyClass();
System.out.println(m);

Expected style of toString output:

Class Name[attribute=value,attribute=value...]

e.g. public class MyClass

{

private int x;
private double y;
x = 0;
y = 3.5;

public String toString()

{

String s;
s = "MyClass[x=" + x + ", y=" + y + "]";
return s;

}

Should return MyClass[x-0,y=3.5]

equals()

-intended to determine whether two objects are equal.
-the == in e.g. m==n is true whenever m and n are objects if and only if m and n point to the same object.
-because of this we need the equals method.

public boolean equals(Object o)
{
MyClass m = (MyClass) o; //this is called a cast.

if ((x==m.x) && (y==m.y))
{return true;}
else {return false;}

}

Use getClass() method to determine whether the classes are equal.

{ if(this.getClass() == o.getClass())
{

MyClass m = (MyClass) o;
.
.
.
}else{return false}

}