Java快速教程--vamei 学习笔记(进阶篇)

感谢vamei,学习链接:http://www.cnblogs.com/vamei/archive/2013/03/31/2991531.html


 

Java进阶01 String类

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/08/3000914.html

字符串操作

 --------------------------------------------------------------------------------------------------------

可以用+实现字符串的连接(concatenate),比如:

"abc" + s

 

字符串的操作大都通过字符串的相应方法实现,比如下面的方法:

 

方法                 效果

s.length()              返回s字符串长度

s.charAt(2)           返回s字符串中下标为2的字符

s.substring(0, 4)          返回s字符串中下标0到4的子字符串

s.indexOf("Hello")          返回子字符串"Hello"的下标

s.startsWith(" ")           判断s是否以空格开始

s.endsWith("oo")            判断s是否以"oo"结束

s.equals("Good World!")       判断s是否等于"Good World!"

               ==只能判断字符串是否保存在同一位置。需要使用equals()判断字符串的内容是否相同。

s.compareTo("Hello Nerd!")    比较s字符串与"Hello Nerd!"在词典中的顺序,

               返回一个整数,如果<0,说明s在"Hello Nerd!"之前;

                      如果>0,说明s在"Hello Nerd!"之后;

                      如果==0,说明s与"Hello Nerd!"相等。

s.trim()              去掉s前后的空格字符串,并返回新的字符串

s.toUpperCase()           将s转换为大写字母,并返回新的字符串

s.toLowerCase()        将s转换为小写,并返回新的字符串

s.replace("World", "Universe")    将"World"替换为"Universe",并返回新的字符串

 


 

Java进阶02 异常处理

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/09/3000894.html

异常处理是在解决问题,同时也是在制造问题。大型项目中,过多、过细的异常处理往往会导致程序变得一团糟。异常处理的设计并不简单,并需要谨慎使用。

package test;

public class Test 
{
    public static void main(String[ ] args)    
    {
        Battery aBattery = new Battery();
        aBattery.chargeBattery(0.5);
        aBattery.useBattery(-0.5);
    }
}

class Battery
{
    /**
     *  increase battery
     */
    public void chargeBattery(double p)
    {
        // power <= 1
        if (this.power + p < 1.)
        {
            this.power = this.power + p;
        }
        else
        {
            this.power = 1.;
        }
    }
    
    /**
     *  consume Battery
     */
    public boolean useBattery(double p)
    {
        try {
            test(p);
        }
        catch(Exception e) 
        {
            System.out.println("catch Exception");
            System.out.println(e.getMessage());
            p = 0.0;
        }
        
        if(this.power >=  p)
        {
            this.power = this.power - p;
            return true;
        }
        else
        {
            this.power = 0.0;
            return false;
        }
    }
    
    /**
     * test usage
     */
    private void test(double p) throws Exception // I just throw.don‘t handle
    {
        if (p < 0) 
        {
            Exception e = new Exception("p must be positive");
            throw e;
        }
    }
    
    private double power = 0.0; // percentage of battery
}

 


 

Java进阶03 IO基础

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/11/3000905.html

package test;

import java.io.*;

public class Test
{
    public static void main(String[] args)
    {
        try {
            BufferedReader br =
              new BufferedReader(new FileReader("file.txt")); 

            String line = br.readLine();

            while (line != null) {
                System.out.println(line);
                line = br.readLine();
            }
            br.close();
        }
        catch(IOException e) {
            System.out.println("IO Problem");
        }
    }
}

Hello World!
Hello Nerd!

 

package test;

import java.io.*;

public class Test
{
    public static void main(String[] args)
    {
        try {
            String content = "Thank you for your fish.";

            File file = new File("new.txt");

            // create the file if doesn‘t exists
            if (!file.exists()) {
                file.createNewFile();
            }

            FileWriter fw = new FileWriter(file.getAbsoluteFile());
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(content);
            bw.close();

        }
        catch(IOException e) {
            System.out.println("IO Problem");
        }
    }
}

 


 

Java进阶04 RTTI

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/14/3013985.html

运行时类型识别(RTTI, Run-Time Type Identification)是Java中非常有用的机制,在Java运行时,RTTI维护类的相关信息。

多态(polymorphism)是基于RTTI实现的。RTTI的功能主要是由Class类实现的。

package test;

public class Test
{
    public static void main(String[] args)
    {
        Human aPerson = new Human();
        Class c1      = aPerson.getClass();
        System.out.println(c1.getName());
        
        Human anotherPerson = new Woman();
        Class c2      = anotherPerson.getClass();
        System.out.println(c2.getName());  

//        Class c3      =  Class.forName("Human");
//        System.out.println(c3.getName());
        /*
         * 这句有问题,  Class c3      =  Class.forName("Human");
         */
        
        Class c4 = Woman.class;
        System.out.println(c4.getName());
    }
}

class Human
{    
    /**
     * accessor
     */
    public int getHeight()
    {
       return this.height;
    }

    /**
     * mutator
     */
    public void growHeight(int h)
    {
        this.height = this.height + h;
    }
private int height; 
}


class Woman extends Human
{
    /**
     * new method
     */
    public Human giveBirth()
    {
        System.out.println("Give birth");
        return (new Human());
    }

}

 


 

Java进阶05 多线程

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/15/3000898.html

多线程(multiple thread)是计算机实现多任务并行处理的一种方式。

在单线程情况下,计算机中存在一个控制权,并按照顺序依次执行指令。单线程好像是一个只有一个队长指挥的小队,整个小队同一个时间只能执行一个任务。

在多线程情境下,计算机中有多个控制权。多个控制权可以同时进行,每个控制权依次执行一系列的指令。多线程好像是一个小队中的成员同时执行不同的任务。

在多线程编程中,要尽力避免竞争条件(racing condition),即运行结果依赖于不同线程执行的先后。线程是并发执行的,无法确定线程的先后,所以我们的程序中不应该出现竞争条件。

创建线程

package test;

public class Test
{
    public static void main(String[] args)
    {
        NewThread thread1 = new NewThread();
        NewThread thread2 = new NewThread();
        thread1.start();         //start thread1
        thread2.start();        //start thread2
    }
}

/**
 *  create new thread by inheriting Thread
 */
class NewThread extends Thread
{
    private static int threadID = 0;    //shared by all
    
    /**
     *  constructor
     */
    public NewThread()
    {
        super("ID: " + (++threadID));
    }
    
    /**
     * convert object to string
     */
    public String toString()
    {
        return super.getName();
    }
    
    /**
     * what dors the thread do?
     */
    public void run()
    {
        System.out.println(this);
    }
}

Runnable

package test;

public class Test
{
    public static void main(String[] args)
    {
        Thread thread1 = new Thread(new NewThread(), "first");
        Thread thread2 = new Thread(new NewThread(), "second");
        thread1.start();         //start thread1
        thread2.start();        //start thread2
    }
}

/**
 *  create new thread by implementing Runnable
 */
class NewThread implements Runnable
{
    /**
     * convert object to string
     */
    public String toString()
    {
        return Thread.currentThread().getName();
    }
    
    /**
     * what dors the thread do?
     */
    public void run()
    {
        System.out.println(this);
    }
}

 售票程序

3个售票亭(Booth)共同售卖100张票(Reservoir)。每个售票亭要先判断是否有余票,然后再卖出一张票。如果只剩下一张票,在一个售票亭的判断和售出两个动作之间,另一个售票亭卖出该票,那么第一个售票亭(由于已经执行过判断)依然会齿形卖出,造成票的超卖。为了解决该问题,判断和售出两个动作之间不能有“空隙”。也就是说,在一个线程完成了这两个动作之后,才能有另一个线程执行。

在Java中,我们将共享的资源置于一个对象中,比如下面r(Reservoir)对象。它包含了总共的票数;将可能造成竞争条件的,针对共享资源的操作,放在synchronized(同步)方法中,比如下面的sellTicket()。synchronized是方法的修饰符。在Java中,同一对象的synchronized方法只能同时被一个线程调用。其他线程必须等待该线程调用结束,(余下的线程之一)才能运行。这样,我们就排除了竞争条件的可能。

在main()方法中,我们将共享的资源(r对象)传递给多个线程:

package test;

public class Test
{
    public static void main(String[] args)
    {
        Reservoir r = new Reservoir(100);
        Booth b1 = new Booth(r);
        Booth b2 = new Booth(r);
        Booth b3 = new Booth(r);
    }
}

/**
 *  contain shared resource
 */
class Reservoir
{
    private int total;
    
    public Reservoir(int t)
    {
        this.total = t;
    }
    
    /**
     * Thread safe method
     * serialize access to Booth.total
     */
    public synchronized boolean sellTicket()
    {
        if(this.total > 0)
        {
            this.total = this.total -1;
            return true;         //        successfully sell one ticket
        }
        else
        {
            return false;        //        no more tickets
        }
    }
}

/**
 *  create new thread by inheriting Thread
 */
class Booth extends Thread
{
    private static int threadID = 0;        // owned by Class object
    private Reservoir release;                    // sell this reservoir 
    private int count = 0;                            // owned by this thread object
    /**
     * constructor
     */
    public Booth(Reservoir r)
    {
        super("ID: " + (++threadID));
        this.release = r;                                    // all threads share the same reservoir
        this.start();
    }
    
    /**
     * convert object to string
     */
    public String toString()
    {
        return super.getName();
    }
    
    /**
     * what does the thread do?
     */
    public void run()
    {
        while(true)
        {
            if(this.release.sellTicket())
            {
                this.count = this.count + 1;
                System.out.println(this.getName() + ": sell 1");
                try
                {
                    sleep((int) Math.random()*100);            //random intervals
                }
                catch (InterruptedException e)
                {
                    throw new RuntimeException(e);
                }
            }
            else
            {
                break;
            }
        }
        System.out.println(this.getName() + "I sold: " + count);
    }

}

 


 

Java进阶06 容器

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/15/3000913.html

package test;

import java.util.*;

public class Test
{
    public static void main(String[] args)
    {
//        Human[] persons = new Human[2];              // array size 2
//        persons[0] = new Human(160);
//        persons[1] = new Human(170);

        int[] a = {1, 2, 3, 7, 9};                   // array size 5
        System.out.println(a[2]);

        String[] names = {"Tom", "Jerry", "Luffy"};  // array size 3
        System.out.println(names[0]);
        
        int[] aFrom = {1, 2, 3, 7, 9}; // array size 5
        int[] aTo  = new int[3];
        System.arraycopy(aFrom, 1, aTo, 0, 3);
        System.out.println(aTo[1]);
        
        System.out.println("表(List)");
        List<String> l1 = new ArrayList<String>();
        l1.add("good");            //   good
        l1.add("bad");                //   good -> bad
        l1.add("shit");                //   good -> bad -> shit
        l1.remove(0);                //   bad -> shit
        System.out.println(l1.get(1));
        System.out.println(l1.size());
        
        System.out.println("集合(set)");
        Set<Integer> s1 = new HashSet<Integer>();
        s1.add(4);                        //[4]
        s1.add(5);                        //[4,5]
        s1.add(4);                        //[4,5]
        s1.remove(5);                //[4]
        System.out.println(s1);
        System.out.println(s1.size());
        
        System.out.println("iterator()方法");
        List<Integer> l2 = new ArrayList<Integer>();
        l2.add(4);
        l2.add(5);
        l2.add(2);
        Iterator i = l2.iterator();
        while(i.hasNext()) {
            System.out.println(i.next());
        }
        
        System.out.println("Map是键值对的集合");
        Map<String, Integer> m1 = new HashMap<String, Integer>();
        m1.put("Vamei", 12);
        m1.put("Jerry", 5);
        m1.put("Tom", 18);
        System.out.println(m1.get("Vamei"));
        /*
         * Map还提供了下面的方法,来返回一个Collection:
         * keySet()  将所有的键转换为Set
         * values()  将所有的值转换为List
         */
    }
}

 

 


 

Java进阶07 嵌套类

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/16/3000896.html

内部类

package test;

public class Test
{
    public static void main(String[] args)
    {
        Human me        = new Human("Vamei");
        Human him       = new Human("Jerry");

        Human.Cup myFirstCup  = me.new Cup();
        Human.Cup mySecondCup = me.new Cup();
        Human.Cup hisCup      = him.new Cup();
        System.out.println(myFirstCup.whosCup());
        System.out.println(mySecondCup.whosCup());
        System.out.println(hisCup.whosCup());
    }
}

class Human
{
    /**
     * inner class
     */
    class Cup
    {
        public String whosCup()
        {
            return name;  // access outer field
        }
    }

    /**
     * constructor
     */
    public Human(String n)
    {
        this.name = n;
    }


    public void changeName(String n)
    {
        this.name = n;
    }

    private String name;
}

 

嵌套static类 

package test;

public class Test
{
    public static void main(String[] args)
    {
        Human.Mongolian him = new Human.Mongolian();
        him.Shout();
    }
}

class Human
{
    /**
     * nested class
     */
    static class Mongolian
    {
        public void Shout()
        {
            System.out.println("Oh...Ho...");
        }
    }
}

 


 

Java进阶08 GUI

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/17/3000908.html

 GUI(Graphical User Interface)提供了图形化的界面,允许用户以图形的方式与系统进行互动。

java布局方式:http://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html

package test;

import javax.swing.*;
import java.awt.*;

public class Test {
    private static void createAndShowGUI() {
        JFrame frame = new JFrame("HelloWorld");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Pane‘s layout
        Container cp = frame.getContentPane();
        cp.setLayout(new FlowLayout());

        // create button
        JButton b1 = new JButton("click me");
        JButton b2 = new JButton("shit");

        // add buttons
        cp.add(b1);
        cp.add(b2);

        // show the window
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        Runnable tr = new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        };
        javax.swing.SwingUtilities.invokeLater(tr);
    }
}

 


 

Java进阶09 事件响应

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/23/3000911.html

package test;

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class Test {
    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Hello");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Pane‘s layout
        Container cp = frame.getContentPane();
        cp.setLayout(new FlowLayout());

     // add interactive panel to Content Pane
        cp.add(new ButtonPanel());

        // show the window
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        Runnable tr = new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        };
        javax.swing.SwingUtilities.invokeLater(tr);
    }
}

/**
 * JPanel with Event Handling
 */
class ButtonPanel extends JPanel
{
    public ButtonPanel()
    {
        JButton yellowButton = new JButton("Yellow");
        JButton redButton = new JButton("Red");
        
        this.add(yellowButton);
        this.add(redButton);
        
        /**
         * register ActionListeners
         */
        ColorAction yellowAction = new ColorAction(Color.yellow);
        ColorAction redAction    = new ColorAction(Color.red);
        
        yellowButton.addActionListener(yellowAction);
        redButton.addActionListener(redAction);
    }
    
    /**
     * ActionListener as an inner class
     */
    private class ColorAction implements ActionListener
    {
        public ColorAction(Color c)
        { 
            backgroundColor = c;
    }
   
    
        /**
         * Actions
         */
        public void actionPerformed(ActionEvent event)
        {
            setBackground(backgroundColor); // outer object, JPanel method
            repaint();
        }
    
        private Color backgroundColor;
    }
}

     


 

Java进阶10 内存管理与垃圾回收

学习链接:http://www.cnblogs.com/vamei/archive/2013/04/28/3048353.html

JVM的垃圾回收是多种机制的混合。JVM会根据程序运行状况,自行决定采用哪种垃圾回收。

我们先来了解"mark and sweep"。这种机制下,每个对象将有标记信息,用于表示该对象是否可到达。当垃圾回收启动时,Java程序暂停运行。JVM从根出发,找到所有的可到达对象,并标记(mark)。随后,JVM需要扫描整个堆,找到剩余的对象,并清空这些对象所占据的内存。

另一种是"copy and sweep"。这种机制下,堆被分为两个区域。对象总存活于两个区域中的一个。当垃圾回收启动时,Java程序暂停运行。JVM从根出发,找到可到达对象,将可到达对象复制到空白区域中并紧密排列,修改由于对象移动所造成的引用地址的变化。最后,直接清空对象原先存活的整个区域,使其成为新的空白区域。

Java快速教程--vamei 学习笔记(进阶篇),古老的榕树,5-wow.com

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