This keyword

[Phillipe Rodrigues]

I,m new to java.Please let me know the meaning of this keyword,how to use it and when to use it.

the example program is below:
public class Pet implements Comparable {
int petId;
String petType;
public Pet(int argPetId, String argPetType) {
petId = argPetId;
this.petType = argPetType;......(1)
}

What can be the idea behind using this keyword at (1).

[amitabh mehra]

To understand this keyword, you can take a look at:this keyword tutorial

[Phillipe Rodrigues]

But would like to know why is it mention at (1) and not at (2)

public Pet(int argPetId, String argPetType) {
this.petType = argPetType;......(1)
petId = argPetId;...............(2)
}

[Gavin Tranter]

public Pet(int argPetId, String argPetType) {
this.petType = argPetType;......(1)
petId = argPetId;...............(2)
}

Its use at one is an attempt to remove ambiguaty, by saying that you are assigning argPetType to the field petType of this (the current object).
I dont think it is really need in that example.
In the example below, both field name and paremeter name are the same, so we need to tell Java that we wish to assign someValue to eh instance variable otherwise Java will just try to assign someValue to itself.

public class X{
   private int someValue;
 
   public X(int someValue){
      this.someValue = someValue;
   }
  
   public void setSomeValue(int someValue){
      this.someValue = someValue;
   }
}

You might, in future, wish to put code tags around your code snippets, as this will perserve the codes formatting and make it easier to read.

[ May 29, 2008: Message edited by: Gavin Tranter ]
[ May 29, 2008: Message edited by: Gavin Tranter ]

[Vikas Kapoor]

Hello Phillipe,

Please use CODE tag to enclose your code.

But would like to know why is it mention at (1) and not at (2)

It's not mandatory. You can remove 'this' from (1) or add it to (2) for this particular case.

I suggest you to go through the tutorial suggested by Amitabh. You will have very clear idea about 'this'.

[Karthikeyan Ramaswamy]

hi,

this keyword is current class's object.

this is a simple term to tell.

----------------------------------
[ May 29, 2008: Message edited by: Karthikeyan Ramaswamy ]

[satishkumar janakiraman]

Originally posted by Gavin Tranter:


Its use at one is an attempt to remove ambiguaty, by saying that you are assigning argPetType to the field petType of this (the current object).
I dont think it is really need in that example.
In the example below, both field name and paremeter name are the same, so we need to tell Java that we wish to assign someValue to eh instance variable otherwise Java will just try to assign someValue to itself.

public class X{
   private int someValue;
 
   public X(int someValue){
      this.someValue = someValue;
   }
  
   public void setSomeValue(int someValue){
      this.someValue = someValue;
   }
}

You might, in future, wish to put code tags around your code snippets, as this will perserve the codes formatting and make it easier to read.

[ May 29, 2008: Message edited by: Gavin Tranter ]

[ May 29, 2008: Message edited by: Gavin Tranter ]

Your explanation is correct. Usually the keyword this is used for referring the current instance. Apart from this, the keyword this can be used to assign values to instance variables where local variables hides the instance variables.

public class X{
   private int someValue;
 
   public X(int someValue){
      this.someValue = someValue;
// If we don't use the keyword[B] this [/B] here, the local variable will hide the instance variable. hence we are using this to refer the instance variable.
   }
  
   public void setSomeValue(int someValue){
      this.someValue = someValue;
// the above comment is applicable here also.
   }
}