Java 7 Usage of #

Do you know "#"? Let me guess, not too familiar. Because in the Java1.4.2 era, "#" is used only in writing the annotated content of Javadoc, to link (@see) to the corresponding class of concrete methods. In addition, we almost never use it when writing code.

However, don't be surprised, after the Java 7 release, "#" may become the most familiar friend of Java programmers! Because a few days ago (Edit note: This translation at the end of November 09, when Sun just announced that Java 7 will contain simple closures), Sun Java Mark Reinhold, chief engineer of SE and OPENJDK, has just announced that Java 7 will add a simplified version of the "Closure" feature, where the key symbol is "#". For this reason, the official release time for Java 7 will be postponed from February 2010 to September.

In Java 7, "#" will let the function method become a first-class citizen of the Java language. Let's look at how to implement the closure with the # syntax:

　　Simple Method Reference Example:

For example, to refer to the Equals method of the string class, you should write this:

String#equals (Object)

Look at one more example:

Java.io.file#exists ()

　　Event Listener 1 (code example, from Cay Horstmann)

Before using closures:

Button.addactionlistener (

New ActionListener () {

public void actionperformed (ActionEvent) {

System.out.println ("hi!"); }

}

);

After using closures:

Button.addactionlistener (# (ActionEvent e) System.out.println ("hi!)");

Event Listener 2 (code example, from FSM)

Before using closures:

public void init () {

JButton button = ...;

Button.addactionlistener (new ActionListener () {

public void actionperformed (ActionEvent ev) {

Handleaction (EV);

}

});

}

public void handleaction (ActionEvent ev) {

Handle Event

}

After using closures:

After using closures:

public void init () {

JButton button = ...;

Button.addactionlistener (This#handleaction (ActionEvent));

}

public void handleaction (ActionEvent ev) {

Handle Event

}