Java自学笔记05—接口与内部类 - 黑马程序员技术交流社区

import java.util.Arrays;
public class HelloJava
{
public static void main(String[] args)
{
Employee[] staff = new Employee[3];
staff[0] = new Employee("Harry Hacker", 35000);
staff[1] = new Employee("Carl Cracker", 75000);
staff[2] = new Employee("Tony Tester", 38000);
Arrays.sort(staff);
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary());
}
}

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public class Employee implements Comparable<Employee>
{
private String name;
private double salary;
public Employee(String n, double s)
{
name = n;
salary = s;
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
public int compareTo(Employee other)
{
return Double.compare(salary, other.salary);
}
}

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可以声明接口变量，接口变量必须引用实现了接口的类对象。
如同类可以被继承，接口也可以被扩展。
接口中的常量被自动设为public static final。
一个类可以实现多个接口，但只能继承一个抽象类。
对象克隆当拷贝一个变量时，原始变量与拷贝变量引用同一个对象。
如果创建一个对象的新的copy，它有自己的内存地址，需要使用clone方法。
如果自定义clone方法，需实现Cloneable接口。

public class HelloJava
{
public static void main(String[] args)
{
try
{
Employee original = new Employee("John Q. Public", 50000);
original.setHireDay(2000, 1, 1);
Employee copy = original.clone();
copy.raiseSalary(10);
copy.setHireDay(2002, 12, 31);
System.out.println("original=" + original);
System.out.println("copy=" + copy);
}
catch (CloneNotSupportedException e)
{
e.printStackTrace();
}
}
}

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import java.util.Date;
import java.util.GregorianCalendar;
public class Employee implements Cloneable
{
private String name;
private double salary;
private Date hireDay;
public Employee(String n, double s)
{
name = n;
salary = s;
hireDay = new Date();
}
public Employee clone() throws CloneNotSupportedException
{
Employee cloned = (Employee) super.clone();
cloned.hireDay = (Date) hireDay.clone();
return cloned;
}
public void setHireDay(int year, int month, int day)
{
Date newHireDay = new GregorianCalendar(year, month - 1, day).getTime();
hireDay.setTime(newHireDay.getTime());
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
public String toString()
{
return "Employee[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";
}
}

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接口与回调
回调是一种常见的程序设计模式，在这种模式中，可以指出某个特定事件发生时应该采取的动作。
例如，可以指出在按下鼠标或选择某个菜单项时应该采取什么行动。

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class HelloJava
{
public static void main(String[] args)
{
ActionListener listener = new TimePrinter();
Timer t = new Timer(10000, listener);
t.start();
JOptionPane.showMessageDialog(null, "Quit program?");
System.exit(0);
}
}
class TimePrinter implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
Date now = new Date();
System.out.println("At the tone, the time is " + now);
Toolkit.getDefaultToolkit().beep();
}
}

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内部类
内部类既可以访问自身的数据域，也可以访问外围类的数据域。
内部类对象有一个隐式引用，指向了创建它的外部类对象。
这个引用在内部类的定义中不可见，编译器修改了所有内部类的构造器，添加一个外部类引用的参数。
内部类可以是私有类。

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class HelloJava
{
public static void main(String[] args)
{
TalkingClock clock = new TalkingClock(1000, true);
clock.start();
JOptionPane.showMessageDialog(null, "Quit program?");
System.exit(0);
}
}
class TalkingClock
{
private int interval;
private boolean beep;
public TalkingClock(int interval, boolean beep)
{
this.interval = interval;
this.beep = beep;
}
public void start()
{
ActionListener listener = new TimePrinter();
Timer t = new Timer(interval, listener);
t.start();
}
private class TimePrinter implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
Date now = new Date();
System.out.println("At the tone, the time is " + now);
if (beep)
Toolkit.getDefaultToolkit().beep();
}
}
}

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局部内部类不能用public或private进行声明，其作用域被限定在声明这个局部类的块中。
局部类可以访问局部变量，前提是局部变量被声明为final。
匿名内部类的语法格式为：
new SuperType(construction parameters)
{
inner class methods and data
}
匿名类不能有构造器，在实现接口的时候，不能有构造参数。

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class HelloJava
{
public static void main(String[] args)
{
TalkingClock clock = new TalkingClock();
clock.start(1000, true);
JOptionPane.showMessageDialog(null, "Quit program?");
System.exit(0);
}
}
class TalkingClock
{
public void start(int interval, final boolean beep)
{
ActionListener listener = new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
Date now = new Date();
System.out.println("At the tone, the time is " + now);
if (beep)
Toolkit.getDefaultToolkit().beep();
}
};
Timer t = new Timer(interval, listener);
t.start();
}
}

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静态内部类不会引用外部类对象，无法访问外部类的数据域。

public class HelloJava
{
public static void main(String[] args)
{
double[] d = new double[20];
for (int i = 0; i < d.length; i++)
d[i] = 100 * Math.random();
ArrayAlg.Pair p = ArrayAlg.minmax(d);
System.out.println("min = " + p.getFirst());
System.out.println("max = " + p.getSecond());
}
}
class ArrayAlg
{
public static class Pair
{
private double first;
private double second;
public Pair(double f, double s)
{
first = f;
second = s;
}
public double getFirst()
{
return first;
}
public double getSecond()
{
return second;
}
}
public static Pair minmax(double[] values)
{
double min = Double.MAX_VALUE;
double max = Double.MIN_VALUE;
for (double v : values)
{
if (min > v) min = v;
if (max < v) max = v;
}
return new Pair(min, max);
}
}

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