Adapter Pattern

Posted 2020-12-13 nedrain

Adapter

An Example

// Voltage220V.java
public class Voltage220V {
    public int output220V(){
        int src = 220;
        System.out.println("Voltage = " + src +"V");
        return src;
    }
}

//Voltage5V.java
public interface Voltage5V {
    public int output5V();
}

// VoltageAdapter.java
public class VoltageAdapter extends Voltage220V implements Voltage5V {
    public int output5V() {
        //get 220v
        int srcV = output220V();
        int dstV = srcV / 44;
        return dstV;
    }
}

// Phone.java
public class Phone {
    public void charging(Voltage5V voltage5V){
        if(voltage5V.output5V() == 5){
            System.out.println("Ok, let‘s charge.");
        }else{
            System.out.println("Too high");
        }
    }
}

// Client.java
public class Client {
    public static void main(String[] args) {
        Phone phone = new Phone();
        phone.charging(new VoltageAdapter());
    }
}

Attention

对象适配器

新的 VoltageAdapter.java 聚合关系

package adapter.objectAdapter;

public class VoltageAdapter implements Voltage5V {
    private Voltage220V voltage220V;

    public VoltageAdapter(Voltage220V voltage220V){
        this.voltage220V = voltage220V;
    }
    public int output5V() {
        int desV = 0;
        if(voltage220V != null){
            int srcV = voltage220V.output220V();
            desV = srcV / 44;
        }
        return desV;
    }
}

//Client.java
public class Client {
    public static void main(String[] args) {
        Phone phone = new Phone();
        phone.charging(new VoltageAdapter(new Voltage220V()));
    }
}

接口适配器

先用抽象类去默认实现接口的所有方法，使用抽象类的类只要用匿名内部类实现某一个方法即可。

//Interface4.java
public interface Interface4 {
    public void m1();
    public void m2();
    public void m3();
    public void m4();
}

// 抽象类 AbsAdapter.java
public abstract class AbsAdapter implements Interface4{
    public void m1() {

    }

    public void m2() {

    }

    public void m3() {

    }

    public void m4() {

    }
}

public class Client {
    public static void main(String[] args) {
       AbsAdapter absAdapter = new AbsAdapter(){
            @Override
            public void m1() {
                System.out.println("This is m1");
            }
        };

        absAdapter.m1();
    }
}

抽象方法不能实例化，但是可以通过匿名内部类的方式使用。