Java Tutorial 12 – Constructors

constructors are a special type of method which we can use to initialize Objects when we create it. If u do not use constructor, objects contains all the variables and methods, But Using constructor you can initialize values of variables. For example you can initialize some variables to zero or Strings to default values and etc. Lets Clear this with an example. Create two classes Tom and Jerry.

Tom:

public class Tom {

public static void main(String[] args){
Jerry object = new Jerry();
object.print();
}
}

Jerry:

public class Jerry {
int a;
String b;

public void print(){
System.out.println(“int a = “+a);
System.out.println(“String b = “+b);
}
}

Now if u run the Tom.java you will see the output like:

int a = 0
String b = null

Now if you want to initialize String b to some text say “Hi” and int a to value 5 whenever the new object is created, you can do it by creating constructor. There are some rules for it:

• Name of the constructor must be same as name of class.
• there is no other rule 😛

Now lets create constructor for Jerry class and initialize variables.

Jerry:

public class Jerry {
int a;
String b;

Jerry(){
a=5;
b = “Hi”;
}
public void print(){
System.out.println(“int a = “+a);
System.out.println(“String b = “+b);
}
}

 

!!!!! yap writing return type and access modifiers is optional. We can define Constructor by just Jerry(){ … }.

Now if you run the Tom.java you will see the output like:

int a = 5
String b = Hi

Here constructor initialized both variables when we created an object of Jerry.

catch you again later…

doubts are invited.

have a nice day.

Peace.