Inheritance
Don't use inheritance just to reuse code.
/**
* Inheritance means that a subclass extends a super class.
* Superclasses defines what subclasses have in common ...
* then abstract those features.
*
* Every class in Java extends class Object.
* Object is the only class that has no superclass.
*/
package com.minte9.oop.inheritance;
public class Inheritance {
public static void main(String[] args) {
Dog dog = new Dog();
dog.setAction("barking");
dog.action(); // The Dog is barking
Bird bird = new Bird();
bird.setAction("flying");
bird.action(); // The Bird is flying
}
}
abstract class Animal {
public String action;
public void setAction(String a) {
action = a;
}
public abstract void action();
}
class Dog extends Animal {
@Override public void action() {
System.out.println(
"The Dog is " + action
);
}
}
class Bird extends Animal {
@Override public void action() {
System.out.println(
"The Bird is " + action
);
}
}
Annotation
Override annotation acts as a compile-time safeguard.
/**
* Abstract method with no Override annotation ...
* will throw error only at compile time.
*/
package com.minte9.oop.inheritance;
public class Annotation {
public static void main(String[] args) {
new MyClass();
}
}
abstract class MyAbstractClass {
abstract public void setName();
}
class MyClass extends MyAbstractClass {
// Wrong method name - with no Override annotation)
public void setNames() {}
// Correct - with Override annotation
@Override
public void setName() {}
}
Super
The super() method is used to call parent constructor.
/**
* super() method is used to call parent constructor
* It must be the first statement in each controller
*/
package com.minte9.oop.inheritance;
public class Super {
public static void main(String[] args) {
new A();
}
}
class A extends ParentClass {
public A() {
super(); // Parent constructor
}
/*
public void A(String s) {
// Wrong, void is the first statement
super(s);
}
*/
}
class ParentClass {
public ParentClass() {
System.out.println("Parent constructor");
}
}
Last update: 496 days ago
