接口的应用

1.为什么要使用接口？

以前所讲的继承例子：

claqss Printer {

void open () {

System.out.println ("open");

}

void close () {

System.out.println ("close");

}

void print (String s) {

System.out.println ("print--->" + s);

}

}

//惠普打印机

class HPPrinter extends Printer {

}

//佳能打印机

claqss CanonPrinter extends Printer  {

void clean() {

System.out.println ("clean");

}

void close () {

this.clean ();

super.close ();

}

}

现在改为接口：

interface Printer {

public void open () ;

public void close ();

public void print (String s);

}

class HPPrinter implements Printer {

public void open () {

System.out.println ("HP open");

}

public void close (){

System.out.println ("HP close");

}

public void print (String s){

System.out.println ("HP print --->" + s);

}

}

class CanonPrinter implements Printer {

private void clean () {

System.out.println ("Canon clean");

}

public void open () {

System.out.println ("Canonopen ");

}

public void close () {

System.out.println ("Canonclose ");

}

public void print (String s) {

System.out.println ("Canonprint --->" + s);

}

}

class Test {

public static void main (String args []) {

//根据用户的选择选择相应的对象，并且向上转型为Pinter类型

Printer printer = null;

int flag = 0;

if (flag = 0){

printer = new HPPrinter ();

}

else if (flag = 1){

printer = new Canonrinter ();

}

printer .open ();

printer .print ("test");

printer .close ();

}

}

如果再添加十个打印机呢，如果再写十个类就太麻烦了，那就需要用的工厂模式了

2.工厂方法模式

class PrinterFactory {

public Printer getPrinter (int flag) {

Printer printer = null;

if (flag = 0){

printer = new HPPrinter ();

}

else if (flag = 1){

printer = new Canonrinter ();

}

return printer;

}

}

其他类相同，只需改变Test 类

class Test {

public static void main (String args []) {

//根据用户的选择选择相应的对象，并且向上转型为Pinter类型

Printer printer = null;

int flag = 0;

Printer printer = PrinterFactory.getPrinter (flag);

printer .open ();

printer .print ("test");

printer .close ();

}

}