One Method
A functional interface has only one abstract method (used as type for lambdas).
/**
* A functional interface has only one abstract method ...
* used as type for lambdas.
*/
package com.minte9.lambdas.functional_interfaces;
import javax.swing.JButton;
import javax.swing.JFrame;
/*
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
*/
public class OneMethod {
public static void main(String[] args) {
JFrame frame = new JFrame();
JButton button = new JButton("Click me");
/*
button.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("Button clicked");
}
}
);
*/
button.addActionListener(event -> { // Look Here
System.out.println("Button clicked");
});
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(button);
frame.setSize(300, 300);
frame.setVisible(true);
}
}
/*
abstract interface ActionListener extends EventListener {
public abstract void actionPerformed(ActionEvent arg0);
}
*/
Predicate
Functional interfaces can come in many forms.
/**
* Examples of functional interfaces, using Predicate interface.
*/
package com.minte9.lambdas.functional_interfaces;
import java.util.function.Function;
import java.util.function.Predicate;
public class Predicates {
public static void main(String[] args) {
Predicate<Integer> op1 = (x) -> (x % 2 == 0);
System.out.println(op1.test(36));
// true
Predicate<String> op2 = new Predicate<>() {
@Override public boolean test(String t) {
return t.length() > 3;
}
};
System.out.println(op2.test("abcd"));
// true
Predicate<String> op3 = t -> (t.length() > 3);
System.out.println(op3.test("abcd"));
// true
Function<Long, Long> op = x -> x + 1;
System.out.println(op.apply(20L));
// 21
}
}
/*
package java.util.function;
public abstract interface Predicate<T> {
public abstract boolean test(T arg0);
...
*/
Custom
You can create custom functional interface.
/**
* You can create custom functional interface.
*/
package com.minte9.lambdas.functional_interfaces;
public class Custom {
public static void main(String[] args) {
MyFuncInterface s1 = s -> s + "!";
MyFuncInterface s2 = s -> s + "?";
System.out.println(s1.run("Hello"));
// Hello!
System.out.println(s2.run("Hello"));
// Hello?
}
}
abstract interface MyFuncInterface {
String run(String s);
}
Last update: 580 days ago
