Default methods
Prior to Java 8, adding new methods to interfaces breaks existing implemenations.
/**
* Starting with Java 8 ...
* interfaces can have default method construct
*/
package com.minte9.effective.interfaces_default;
public class DefaultMethods {
public static void main(String[] args) {
new Login().subscribe();
// Default subscribe method
new Subscribe().subscribe();
// Default subscribe method - overwritten
}
}
interface Commandable {
public abstract void getCommand();
public default void subscribe() { // Look Here
System.out.println("Default subscribe method");
}
}
class Subscribe implements Commandable {
@Override public void getCommand() {
}
@Override public void subscribe() {
System.out.println("Default subscribe method - overwritten");
}
}
/**
* Old class - don't need to imnplement subscribe()
*/
class Login implements Commandable {
@Override public void getCommand() {
}
//subscribe() overwitten - not needed!
}
Contract
An interface is a contract, don't use interfaces for inheritance!
/**
* Default methods for existing interfaces ...
* should be avoided unless the need is critical.
*
* A default method added to an interface break main scope ...
* which is to unsure a valid contract betwween classes.
*/
package com.minte9.effective.interfaces_default;
public class Contract {
public static void main(String[] args) {
new Subscribe();
}
}
interface A {
public default void getCommand() {
}
public default void subscribe() {
}
}
class B implements A {
// there is no need to override subscribe() so ...
// the contract is no longer valid!
}
Last update: 595 days ago
