Adapter(适配器)模式

适配器模式保留现有类所提供的服务，向客户提供接口，以满足客户的期望。适配器模式可分为类适配器模式、对象适配器模式和标识适配器模式三种。

类适配器模式
拓展一个现有的类，并实现一个目标接口，将把客户的调用转变为调用现有类的方法。

对象适配器模式
拓展一个目标类，并把它委派给一个现有的类，将客户调用转发给现有类的实例。

• 如果希望适配的方法没有在接口中指定时，就应该使用委托方式，而不是创建子类方式。即对象适配器模式。
• 只要我们所适配的接口可以得到抽象类的支持，也必须使用对象适配器模式。
• 如果适配器类需要从多个对象中提取信息，也应当使用对象适配器。

Swing中的JTable组件是应用对象适配器模式的很好例子。JTable组件通过调用TableModel接口中定义的方法获取表格
的相关信息，这样就可以很容易地写出一个适配器类，从域对象中获取用于填充表格的数据。

import javax.swing.table.*;
/**
 * Adapt a collection of rockets for display in a JTable.
 * 
 * @author Steven J. Metsker
 */
public class RocketTableModel extends AbstractTableModel {
    protected Rocket[] rockets;
    protected String[] columnNames = new String[] { "Name", "Price", "Apogee" };

    /**
     * Construct a rocket table from an array of rockets.
     * 
     * @param rockets
     *            an array of rockets
     */
    public RocketTableModel(Rocket[] rockets) {
        this.rockets = rockets;
    }

    /**
     * @return the number of columns in this table.
     */
    public int getColumnCount() {
        return columnNames.length;
    }

    /**
     * @param index
     *            which column is interesting
     * @return the name of the indicated column
     */
    public String getColumnName(int i) {
        return columnNames[i];
    }

    /**
     * @return the number of rows in this table.
     */
    public int getRowCount() {
        return rockets.length;
    }

    /**
     * @param row
     *            which row is interesting
     * @param col
     *            which column is interesting
     * @return the value at the indicated row and column.
     */
    public Object getValueAt(int row, int col) {
        switch (col) {
        case 0:
            return rockets[row].getName();
        case 1:
            return rockets[row].getPrice();
        case 2:
            return new Double(rockets[row].getApogee());
        default:
            return null;
        }
    }
}

import java.awt.Component;
import java.awt.Font;

import javax.swing.*;
public class ShowRocketTable { 
    public static void main(String[] args) {
        setFonts();
        JTable table = new JTable(getRocketTable());
        table.setRowHeight(36);
        JScrollPane pane = new JScrollPane(table);
        pane.setPreferredSize(new java.awt.Dimension(300, 100));
        display(pane, " Rockets");
    }
    public static void display(Component c, String title) {
        JFrame frame = new JFrame(title);
        frame.getContentPane().add(c);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
        frame.pack();
        frame.setVisible(true);
    }

    private static RocketTableModel getRocketTable() {
        Rocket r1 = new Rocket("Shooter", 1.0, new Dollars(3.95), 50.0, 4.5);
        Rocket r2 = new Rocket("Orbit", 2.0, new Dollars(29.03), 5000, 3.2);
        return new RocketTableModel(new Rocket[] { r1, r2 });
    }

    private static void setFonts() {
        Font font = new Font("Dialog", Font.PLAIN, 18);
        UIManager.put("Table.font", font);
        UIManager.put("TableHeader.font", font);
    }
}

public class Dollars {
    public static final Dollars cent = new Dollars(0.01);

    static final int CENTS_PER_DOLLAR = 100;

    long cents;

    public Dollars(double value) {
        this.cents = Math.round(value * CENTS_PER_DOLLAR);
    }

    public boolean isZero() {
        return cents == 0;
    }

    public Dollars plus(Dollars that) {
        return new Dollars(1.0 * (this.cents + that.cents) / CENTS_PER_DOLLAR);
    }

    public Dollars times(int multiplier) {
        return new Dollars((this.cents * multiplier) / CENTS_PER_DOLLAR);
    }

    public Dollars dividedBy(int divisor) {
        double newCents = (1.0 * cents / divisor) / CENTS_PER_DOLLAR;
        return new Dollars(newCents);
    }

    public double dividedBy(Dollars that) {
        return (1.0 * this.cents) / that.cents;
    }

    public boolean isLessThan(Dollars that) {
        return this.cents < that.cents;
    }

    public String toString() {
        StringBuffer result = new StringBuffer("$");

        long dollars = cents / CENTS_PER_DOLLAR;
        result.append(dollars);
        result.append(‘.‘);

        long pennies = cents % CENTS_PER_DOLLAR;
        if (pennies < 10) result.append(‘0‘);
        result.append(pennies);

        return result.toString();
    }

    public boolean equals(Object obj) {
        if (!obj.getClass().equals(this.getClass()))
            return false;
        Dollars that = (Dollars) obj;
        return this.cents == that.cents;
    }

    public int hashCode() {
        return (int) cents;
    }

    public long asCents() {
        return cents;
    }
}

public class Rocket extends Firework {
    private double apogee;

    private double thrust;

    /**
     * Allow creation of empty objects to support reconstruction from persistent
     * store.
     */
    public Rocket() {
    }

    /**
     * Create a rocket with all its expected properties. See the superclass for
     * descriptions of other parameters
     * 
     * @param apogee
     *            The height (in meters) that the rocket is expected to reach
     * @param thrust
     *            The rated thrust (or force, in newtons) of this rocket
     */
    public Rocket(String name, double mass, Dollars price, double apogee,
            double thrust) {
        super(name, mass, price);
        setApogee(apogee);
        setThrust(thrust);
    }

    /**
     * The height (in meters) that the rocket is expected to reach.
     */
    public double getApogee() {
        return apogee;
    }

    public void setApogee(double value) {
        apogee = value;
    }

    /**
     * The rated thrust (or force, in newtons) of this rocket.
     */
    public double getThrust() {
        return thrust;
    }

    public void setThrust(double value) {
        thrust = value;
    }
}

public class Firework {
    /**
     * @return a firework of the given name. This method supports a "Strategy"
     *         example, but it isn‘t really implemented.
     * @param name
     *            a name to lookup
     */
    public static Firework lookup(String name) {
        return new Firework(name, 9.0, new Dollars(3));
    }

    /**
     * @return a random firework from our shelves. This method is not actually
     *         implemented -- it‘s here as part of a "Strategy" example.
     */
    public static Firework getRandom() {
        return new Firework("Random firework", 10.0, new Dollars(15));
    }


    private String name;
    private double mass;
    private Dollars price;

    /**
     * Allow creation of empty objects to support reconstruction from persistent
     * store.
     */
    public Firework() {
    }
    public Firework(String name, double mass, Dollars price) {
        setName(name);
        setMass(mass);
        setPrice(price);
    }

    /**
     * The unique name of this type of firework
     */
    public String getName() {
        return name;
    }

    public void setName(String value) {
        name = value;
    }

    /**
     * The mass, in kilograms, of one instance of this type
     */
    public double getMass() {
        return mass;
    }

    public void setMass(double value) {
        mass = value;
    }

    /**
     * The price (in dollars) of one instance of this type
     */
    public Dollars getPrice() {
        return price;
    }

    public void setPrice(Dollars value) {
        price = value;
    }

    /**
     * @return a textual representation of this firework.
     */
    public String toString() {
        return getName();
    }
}

JTable类有两个原因不能使用类适配器：

1. 表适配器必须拓展现AbstractTableModel类，应此它不能再拓展现有的类；
2. JTable类需要收集多个对象的数据，只有对象适配器才可以对多个对象进行适配。

标识适配器模式
创建存根类MouseAdapter以后，在实现鼠标监听器类的时候，就不用实现MouseAdapter接口的所有方法