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- Written by Nam Ha Minh
- Last Updated on 18 August 2019   |   Print Email
This article helps you understand what is
abstract keyword in Java and how to use it in the Java programming language.You know, the
abstract keyword is used to declare a class or a method as abstract. An abstract class can have abstract methods which have to be implemented by its sub classes. An abstract method does not have concrete implementation or body, and must ends with a semicolon. The following example declares a class
Car as abstract:
public abstract class Car {
public abstract void drive();
}
The method
drive() is also declared as abstract.
1. Some rules for abstract class and abstract method:
An abstract class:
- cannot be instantiated by the new keyword. The purpose of an abstract class is to be inherited by derived classes.
- can have both abstract and non-abstract methods.
An abstract method:
- does not have body and must end with a semicolon.
- must be implemented by concrete sub classes.
- makes the enclosing class must be declared as abstract also
2. Java abstract class and method example
A class that extends the abstract
Car class and implements its abstract method:
class PoliceCar extends Car {
public void drive() {
// drive faster than normal car
}
}
An abstract class has both abstract and non-abstract methods:
abstract class Airplane {
public abstract void takeOff();
public void landing() {
// landing smoothly
}
}
See
all keywords in Java.
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About the Author:
Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He started programming with Java in the time of Java 1.4 and has been falling in love with Java since then. Make friend with him on
Facebook and watch
his Java videos you YouTube.