Flash cards
Review the key moves
What is the main idea behind Java Interface?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
// ___ interface Animal { public void animalSound(); // interface method (does not have a body) public void run(); // interface method (does not have a body)Put the learning moves in the order that makes the concept easiest to apply.
Interfaces
Another way to achieve abstraction in Java, is with interfaces.
An interface is a completely " abstract class " that is used to group related methods with empty bodies:
Example
// interface interface Animal { public void animalSound(); // interface method (does not have a body) public void run(); // interface method (does not have a body)
}To access the interface methods, the interface must be "implemented" (kinda like inherited) by another class with the implements keyword (instead of extends ). The body of the interface method is provided by the "implement" class:
Example
// Interface interface Animal { public void animalSound(); // interface method (does not have a body) public void sleep(); // interface method (does not have a body)
}
// Pig "implements" the Animal interface class Pig implements Animal { public void animalSound() { // The body of animalSound() is provided here System.out.println("The pig says: wee wee");
}
public void sleep() {
// The body of sleep() is provided here System.out.println("Zzz");
}
}
class Main {
public static void main(String[] args) {
Pig myPig = new Pig(); // Create a Pig object
myPig.animalSound();
myPig.sleep();
}
}- Like abstract classes , interfaces cannot be used to create objects (in the example above, it is not possible to create an "Animal" object in the MyMainClass)
- Interface methods do not have a body - the body is provided by the "implement" class
- On implementation of an interface, you must override all of its methods
- Interface methods are by default abstract and public
- Interface attributes are by default public , static and final
- An interface cannot contain a constructor (as it cannot be used to create objects)
1) To achieve security - hide certain details and only show the important details of an object (interface).
2) Java does not support "multiple inheritance" (a class can only inherit from one superclass). However, it can be achieved with interfaces, because the class can implement multiple interfaces. Note: To implement multiple interfaces, separate them with a comma (see example below).
Multiple Interfaces
To implement multiple interfaces, separate them with a comma:
Example
interface FirstInterface {
public void myMethod(); // interface method
}
interface SecondInterface {
public void myOtherMethod(); // interface method
}
class DemoClass implements FirstInterface, SecondInterface {
public void myMethod() {
System.out.println("Some text..");
}
public void myOtherMethod() {
System.out.println("Some other text...");
}
}
class Main {
public static void main(String[] args) {
DemoClass myObj = new DemoClass();
myObj.myMethod();
myObj.myOtherMethod();
}
}