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Constructors in Java
Constructors are used every time to initialize instance variables. There are some additional rules associated with constructors that are often asked in interviews.Hence revising those here through a blog post.
2.When an object of an class is created,JVM goes to the class and searches for that matching constructor.
class A{
A(){ //default no arg constructor
}}
4.A programmer can have multiple constructors in a class provided their signatures are different this is called constructor overloading.
class A{
A(){
//some code
}
A(int x){
//some code
}
A(float x){
//some code
}
A(float x,int y){
//some code
}
A(int x,float y){
}
A(int z){}//THIS WILL GIVE COMPILE ERROR SInce its already defined on top.
}
A a=new A();
new A();//goes to first matching constructor
5.JVM always calls the matching constructor from the class.HOWEVER,a programmer can call other constructors of this class by using the the this() method
class A{
A(){
System.out.println("A"); //I
A(int x){
this(); //this will go to constructor A();
System.out.println("AA"); //II
}
}
class App{
public static void main(String[]args){
new A(5);
}}
OUTPUT:
A
AA
6.If a programmer desires it can call the constructor of the super class as well from its own constructor using the super() method.
class A{
A(){
System.out.println("A"); //I
}
}
class B extends A{
B(){
super(); //this is called implicitly refer next point also
System.out.println("B");
}}
class HelloWorld {
public static void main(String[] args) {
new B();
}
}
OUTPUT:
A
B
7.Whenever a programmer creates a constructor ,JVM writes super() in every constructor implicitly as its first line.
Note:If a class does not extend any class it by default extends the Object class.
Do Try this code in your ide to see it for yourself
class A{
A(){
//super will be called implicitly at the first line of this constructor and here since it does not extend any class it will extend the Object class
System.out.println("A"); //I
}
A(int x){
//super will be called implicitly at the first line of this constructor
System.out.println("AA");
}}
class HelloWorld {
public static void main(String[] args) {
new A(5);
}
}
OUTPUT:
A
AA
That's all for constructors in Java. If any mistake content or otherwise feel free to let me know in the comment section.
Happy Learning :)
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