Code

1、两个线程加两个线程减

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
两个线程加两个线程减
*/
public class ThreadTest3 {
    private static int j;
    private static final Lock lock = new ReentrantLock();

    public static void main(String[] args) {
        for (int i = 0; i < 2; i++){
            new Thread(new Runnable() {
                public void run() {
                    while (true) {
                        lock.lock();
                        try {
                    System.out.println(Thread.currentThread().getName()+"j--=" + j--);
                        } finally {
                            lock.unlock();
                        }
                    }
                }
            }).start();

            new Thread(new Runnable() {
                public void run() {
                    while (true) {
                        lock.lock();
                        try {
                    System.out.println(Thread.currentThread().getName()+"j++=" + j++);
                        } finally {
                            lock.unlock();
                        }
                    }
                }
            }).start();
        }
    }
}

2、子线程循环10次，接着主线程循环100，接着又回到子线程循环10次，接着再回到主线程又循环100，如此循环50次

package com.zhang.thread;

/**
 * @author zhangjinru
 *子线程循环10次，接着主线程循环100，接着又回到子线程循环10次，接着再回到主线程又循环100，如此循环50次
 */

public class ThreadTest2 {
    public static void main(String[] args) {
        new ThreadTest2().init();
    }

    public void init() {
        Business business = new Business();
        new Thread(new Runnable() {
            public void run() {
                for (int i = 1; i <= 50; i++) {
                    business.SubThread(i);
                }
            }
        }).start();

        for (int i = 1; i <= 50; i++) {
            business.MainThread(i);
        }
    }

    private class Business {
        boolean bShouldSub = true;// 这里相当于定义了控制该谁执行的一个信号灯

        public synchronized void MainThread(int i) {

            if (bShouldSub)
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            for (int j = 0; j < 100; j++) {
            System.out.println(Thread.currentThread().getName() + ":第" + i + "次,j=" + j);
            }
            bShouldSub = true;
            this.notify();
        }

        public synchronized void SubThread(int i) {

            if (!bShouldSub)
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            for (int j = 0; j < 10; j++) {
            System.out.println(Thread.currentThread().getName() + ":第" + i + "次,j=" + j);
            }
            bShouldSub = false;
            this.notify();
        }
    }
}

3、Socket套接字

网络上具有唯一标识的IP地址和端口组合在一起才能构成唯一能识别的标识符套接字。

Socket原理机制：

通信的两端都有Socket

网络通信其实就是Socket间的通信

数据在两个Socket间通过IO传输

4、Java中的socket编程（基于TCP/IP协议）

客户端编写：

创建一个Socket实例：构造函数向指定的远程主机和端口建立一个TCP连接；

通过套接字的I/O流与服务端通信；

使用Socket类的close方法关闭连接。

public class ClientSocket {
  public static void main(String args[]) {
        String host = "127.0.0.1";
        int port = 8919;
        try {
          Socket client = new Socket(host, port);
          Writer writer = new OutputStreamWriter(client.getOutputStream());
          writer.write("Hello From Client");
          writer.flush();
          writer.close();
          client.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
    }
}

上面代码中，host即客户端需要连接的机器，port就是服务器端用来监听请求的端口。在选择端口时，需要注意一点，就是0~1023这些端口都已经被系统预留了。这些端口为一些常用的服务所使用，比如邮件，FTP和HTTP。当你在编写服务器端的代码，选择端口时，请选择一个大于1023的端口。

服务器端编写：

创建一个ServerSocket实例并指定本地端口，用来监听客户端在该端口发送的TCP连接请求；

重复执行：

• 调用ServerSocket的accept（）方法以获取客户端连接，并通过其返回值创建一个Socket实例；

• 为返回的Socket实例开启新的线程，并使用返回的Socket实例的I/O流与客户端通信；

• 通信完成后，使用Socket类的close（）方法关闭该客户端的套接字连接。

public class ServerClient {
 public static void main(String[] args) {
       int port = 8919;
       try {
           ServerSocket server = new ServerSocket(port);
         while(true){
           Socket socket = server.accept();
           Reader reader = new InputStreamReader(socket.getInputStream());
           char chars[] = new char[1024];
           int len;
           StringBuilder builder = new StringBuilder();
           while ((len=reader.read(chars)) != -1) {
              builder.append(new String(chars, 0, len));
          }
           System.out.println("Receive from client message=: " + builder);
        }               
           reader.close();
           socket.close();
           server.close();
      } catch (Exception e) {
           e.printStackTrace();
      }
}
}

上面的代码创建了一个服务器端的socket，然后调用accept方法监听并获取客户端的请求socket。accept方法是一个阻塞方法，在服务器端与客户端之间建立联系之前会一直等待阻塞。

 

5、简单的Socket通讯（面试）

客户端：

package com.zhang.socket;
​
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
//没有关闭流
public class test1 {
public static void main(String[] args) {
​
try {
Socket socket = new Socket("127.0.0.1", 8888);
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
new Thread(new Runnable() {
@Override
public void run() {
try {
while (true) {
try {
Thread.sleep(5000);
dataOutputStream.writeUTF("哈哈哈");
dataOutputStream.flush();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
​
new Thread(new Runnable() {
public void run() {
try {
while (true) {
String str = dataInputStream.readUTF();
System.out.println(str);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
} catch (Exception e) {
e.printStackTrace();
}
}
}

服务端：

package com.zhang.socket;
​
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
//没有关闭流
public class test2 {
public static void main(String[] args) {
try {
ServerSocket serverSocket = new ServerSocket(8888);
while (true) {
System.out.println("等待连接");
Socket socket = serverSocket.accept();
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
​
new Thread(new Runnable() {
public void run() {
try {
while (true) {
String str = dataInputStream.readUTF();
System.out.println(str);
dataOutputStream.writeUTF("客户端发来的:" + str);// 读出了后再写回去
dataOutputStream.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
​
}
} catch (Exception e) {
e.printStackTrace();
}
​
}
}

6、Socket的多人聊天室

客户端：

package com.zhang.socket;
​
import java.awt.BorderLayout;
import java.awt.Frame;
import java.awt.TextArea;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.SocketException;
​
public class ChatClient extends Frame {
private static final long serialVersionUID = 1L;
private TextArea ta = new TextArea();
private TextField tf = new TextField();
private DataOutputStream dos = null;
private DataInputStream dis = null;
private Socket socket = null;
private boolean bConnected = false;
private Thread thread = null;
​
public static void main(String[] args) {
new ChatClient().frameClient();
}
​
public void frameClient() {
setSize(400, 400);
setLocation(400, 300);
add(ta, BorderLayout.NORTH);
add(tf, BorderLayout.SOUTH);
pack();//Frame 布局
tf.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
String strMsg = tf.getText();
tf.setText("");
try {
dos.writeUTF(strMsg);
dos.flush();
} catch (IOException e1) {
e1.printStackTrace();
}
}
});
// 关闭窗口事件监听
this.addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
disconnected();
System.exit(0);
}
});
this.connect();
setVisible(true);
}
​
// 链接服务器地址
private void connect() {
try {
socket = new Socket("127.0.0.1", 8888);
dos = new DataOutputStream(socket.getOutputStream());
dis = new DataInputStream(socket.getInputStream());
thread = new Thread(new ChatThread());
thread.start();
} catch (Exception e) {
e.printStackTrace();
}
}
​
// 断开连接
private void disconnected() {
bConnected = false;
try {
dos.close();
dis.close();
socket.close();
} catch (IOException e1) {
e1.printStackTrace();
}
}

// 开启线程接受服务器信息
private class ChatThread implements Runnable {
@Override
public void run() {
try {
bConnected = true;
while (bConnected) {
String msg = dis.readUTF();
String taText = ta.getText();
ta.setText(taText + msg + "
");
}
} catch (SocketException e) {
System.out.println("退出");
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

服务端：

package com.zhang.socket;
​
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
​
public class ChatServer {
private boolean started = false;
private List<ChatThread> chatThreads = new ArrayList<ChatThread>();
​
public static void main(String[] args) {
new ChatServer().startServer();
}
​
private void startServer() {
ServerSocket serverSocket=null;
try {
// 开启服务端Socket
serverSocket = new ServerSocket(8888);
started = true;
while (started) {
// 接受客户端连接请求
Socket socket = serverSocket.accept();
String RemoteIP =socket.getInetAddress().getHostAddress();
String RemotePort = ":"+socket.getLocalPort();
System.out.println("客户端"+RemoteIP+RemotePort+"已连接");
// 开启线程处理客户端通信
ChatThread ct = new ChatThread(socket);
chatThreads.add(ct);
new Thread(ct).start();
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
serverSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
​
private class ChatThread implements Runnable {
private Socket socket;
private DataInputStream din = null;
private DataOutputStream don = null;
private boolean bConnected = false;
​
public ChatThread(Socket socket) {
this.socket = socket;
}
​
// 发送信息的函数
private void send(String strMsgIn) {
try {
don.writeUTF(strMsgIn);
don.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
​
@Override
public void run() {
try {
din = new DataInputStream(socket.getInputStream());
don = new DataOutputStream(socket.getOutputStream());
// 读取数据
bConnected = true;
while (bConnected) {
String strMsgIn = din.readUTF();
System.out.println(strMsgIn);
// 接收到数据后发送给每个客户端
for (int i = 0; i < chatThreads.size(); i++) {
chatThreads.get(i).send(strMsgIn);
}
}
} catch (IOException e) {
try {
// 如果客户端出错或关闭，直接关闭连接，并移除List中的当前线程
socket.close();
chatThreads.remove(this);
} catch (IOException e1) {
e1.printStackTrace();
}
} finally {
try {
din.close();
don.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
​
}
}

7、文件的基本操作 

package com.zhang.thread;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

public class IOTest {
    public static void main(String[] args) throws Exception {
        ReadFile();
        WriteFile();
        CopyPicture("pic.jpg", "哈哈哈.jpg");
        CopyFile("a.txt", "f.txt");
    }

    /**
     * 写文件
     */
    private static void WriteFile() {
        String s= "哈哈哈";
        try {
            //字节流写入文件
            FileOutputStream fos = new FileOutputStream("1.txt");
            fos.write(s.getBytes("UTF-8"));
            fos.close();

            // 字符流写入文件
            FileWriter fw = new FileWriter("1.txt");
            fw.write(s);
            fw.close();

            // 字符流写入文件
            PrintWriter pw = new PrintWriter("1.txt", "utf-8");
            pw.write(s);
            pw.close();

            //通过缓存写数据
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("2.txt")), "UTF-8"));
            for (int i = 1; i < 100; i++) {
                bw.write("哈哈哈" + i);
                bw.newLine();
            }
            bw.close();
        } catch (Exception e) {
            System.err.println("write errors :" + e);
        }

    }

    /**
     * 读文件
     */
    private static void ReadFile() {
        StringBuilder result = new StringBuilder();
        try {
            //通过字符流读文件
            FileReader fr = new FileReader("2.txt");
            char[] buf = new char[1024];
            int len =0;
            while((len=fr.read(buf))!=-1){
                String myStr = new String(buf, 0, len);
                System.out.println(myStr);
            }
            fr.close();

            // 字节流读文件
            FileInputStream frs = new FileInputStream("1.txt");
            byte[] bufs = new byte[1024];
            int lens = 0;
            while((lens=frs.read(bufs))!=-1){
                String myStrs=new String(bufs, 0, lens,"UTF-8");
                System.out.println(myStrs);
            }
            frs.close();

            //通过缓存读书节    
//            BufferedReader bf = new BufferedReader(new FileReader("names.txt"));
            BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(new File("1.txt")), "UTF-8"));
            String lineTxt = null;
            while ((lineTxt = br.readLine()) != null) {
                System.out.println(lineTxt);
                result.append(lineTxt+"
");
            }
            br.close();
            System.out.println(result.toString());
        } catch (Exception e) {
            System.err.println("read errors :" + e);
        }
    }
    
    /**
     * 通过字节流复制文件，可以复制文本文件和二进制文件，如图片
     * @param oldfile
     * @param newfile
     * @throws Exception
     */
    private static void CopyPicture(String oldfile, String newfile) throws Exception {
        int len = 0;
        byte[] buf = new byte[1024];
        BufferedInputStream bufferedInputStream =new BufferedInputStream(new FileInputStream(new File(oldfile)));
        BufferedOutputStream bufferedOutputStream =new BufferedOutputStream(new FileOutputStream(new File(newfile)));
        while ((len = bufferedInputStream.read(buf)) != -1) {
            bufferedOutputStream.write(buf, 0, len);
        }
        bufferedInputStream.close();
        bufferedOutputStream.close();
    }

    /**
     * 通过字符流复制文件，只能复制文本文件，如果复制二进制文件会出错
     * @param oldfile
     * @param newfile
     * @throws Exception
     */
    private static void CopyFile(String oldfile, String newfile) throws Exception{
        BufferedReader bufferedReader =new BufferedReader(new InputStreamReader(new FileInputStream(new File(oldfile)), "UTF-8"));
        BufferedWriter bufferedWriter =new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File(newfile)),"UTF-8"));
        String len=null;
        while((len=bufferedReader.readLine())!=null){
            bufferedWriter.write(len);
            bufferedWriter.newLine();
        }
        bufferedReader.close();
        bufferedWriter.close();
    }    
}

 8、将a.txt文件中的单词与b.txt文件中的单词交替合并到c.txt文件中，a.txt文件中的单词用回车符分隔，b.txt文件中用回车或空格进行分隔。

public static void main(String[] args) throws Exception {
FileManager a = new FileManager("a.txt", new char[] { '
' });
FileManager b = new FileManager("b.txt", new char[] { '
', ' ' });
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("c.txt")), "UTF-8"));
String aWord = null;
String bWord = null;
while ((aWord = a.nextWord()) != null) {
bufferedWriter.write(aWord);
bufferedWriter.newLine();
if ((bWord = b.nextWord()) != null) {
bufferedWriter.write(bWord);
bufferedWriter.newLine();
}
}
while ((bWord = b.nextWord()) != null) {
bufferedWriter.write(bWord);
bufferedWriter.newLine();
}
bufferedWriter.close();
}
}
​
class FileManager {
String[] words = null;
int pos = 0;
FileManager(String filename, char[] seperators) throws Exception {
StringBuilder builder = new StringBuilder();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream(new File(filename)), "UTF-8"));
char[] buf = new char[1024];
int len = 0;
while ((len = bufferedReader.read(buf)) != -1) {
builder.append(new String(buf, 0, len));
}
bufferedReader.close();
String regex = null;
if (seperators.length > 1) {
regex = "" + seperators[0] + "|" + seperators[1];
} else {
regex = "" + seperators[0];
}
words = builder.toString().split(regex);
}
​
public String nextWord() {
if (pos == words.length){
return null;
}
return words[pos++];
}

9、查找Java文件夹下的全部.java文件，并复制到jad文件夹下后缀改为.jad

File srcDir = new File("java");
if (!(srcDir.exists() && srcDir.isDirectory())){
System.out.println("目录不存在");
}
File[] files = srcDir.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.endsWith(".java");
}
});
System.out.println(files.length);
File destDir = new File("jad");
if (!destDir.exists())
destDir.mkdir();
for (File f : files) {
BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(f) );
String destFileName = f.getName().replaceAll("\.java$", ".jad");// \.java$ 正则表达式 结尾为.java的文件
BufferedOutputStream bufferedOutputStream =new BufferedOutputStream(new FileOutputStream(new File(destDir,destFileName)));
copy(bufferedInputStream, bufferedOutputStream);
bufferedInputStream.close();
bufferedOutputStream.close();
}
}
​
private static void copy(BufferedInputStream ips, BufferedOutputStream ops) throws Exception {
int len = 0;
byte[] buf = new byte[1024];
while ((len = ips.read(buf)) != -1) {
ops.write(buf, 0, len);
}
}

10、编写一个截取字符串的函数，输入为一个字符串和字节数，输出为按字节截取的字符串，但要保证汉字不被截取半个如“我ABC”，4，应该截取“我AB”，输入“我ABC汉DEF”，6，应该输出“我ABC”，而不是“我ABC+汉的半个”

public static void main(String[] args) throws Exception {
String str = "我a爱中华abc我爱哈奥def";
       //中文一个字占2个字节，UTF-8占3个字节。中文的字节码为负数。
int num = trimGBK(str.getBytes("GBK"), 7);
System.out.println(str.substring(0, num));
}
​
public static int trimGBK(byte[] buf, int n) {
int num = 0;
boolean bChineseFirstHalf = false;
for (int i = 0; i < n; i++) {
if (buf[i] < 0 && !bChineseFirstHalf) {
bChineseFirstHalf = true;
} else {
num++;
bChineseFirstHalf = false;
}
}
return num;
}

11、分别统计英文字符的数量，中文字符的数量，和数字字符的数量，假设字符中没有中文字符、英文字符、数字字符之外的其他特殊字符

public static void main(String[] args) throws Exception {
String str = "应该23vr输出我ABC而不是我ABC6tad73592汉的半个";
int engishCount = 0;
int chineseCount = 0;
int digitCount = 0;
​
for (int i = 0; i < str.length(); i++) {
char ch = str.charAt(i);
if (ch >= '0' && ch <= '9') {
digitCount++;
} else if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
engishCount++;
} else {
chineseCount++;
}
}
System.out.println(engishCount + "***" + chineseCount + "****" + digitCount);
}

12、字符串匹配算法

String str1 ="abcdefg";
    String str2= "cde";
    char[] c1 = str1.toCharArray();
    char[] c2=str2.toCharArray();
    int i1=c1.length;
    int i2=c2.length;
    for (int i = 0; i < i1-i2; i++) {
        int j=0;
        while(j<i2&&c2[j]==c1[i+j]){
            j++;
            if(j==i2){
                return 1;
            }
        }
    }
   return 0;

13、打印*

private static void printstart(){
        for(int i=1;i<=5;i++){//i--控制行
            for(int j=5-i;j>=0;j--){//j--控制空格的数量
                System.out.print(" ");
            }
            for(int k=1;k<=2*i-1;k++){//k--控制*的数量
                System.out.print("*");
            }
            System.out.println();//每循环一次换行
        }
    }

14、计算1+11+111+1111+11111的和

private static void Sum(){
        int a=0,sum=0;
        for(int n=1;n<=5;n++)
        {
            a=(a*10)+1;
            System.out.println(a);
            sum+=a;
        }
        System.out.print("sum="+sum);
    }

15、水仙花数

private static void shuixuanhua(){
        for(int i=100;i<1000;i++){  
            int ge  = i%10;  
            int shi = i/10%10;  
            int bai = i/10/10%10;  
            if(i == (ge*ge*ge+shi*shi*shi+bai*bai*bai)){  
                System.out.println(i);  
            }  
        }        
    }

16、map遍历

private static void listmap(){
        Map<Integer, Integer> map=new HashMap<>();
        map.put(0, 1);
        map.put(2, 3);
        map.put(4, 5);
        map.put(6, 7);
        map.put(8, 9);
        for (Integer key :map.keySet()) {
            System.out.println(key);
        }
        for (Integer key :map.values()) {
            System.out.println(key);
        }
    }

 17、连接MySQL数据库

 private static void jdbc() {
        Connection conn = null;
        PreparedStatement preparedStatement = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "123");
            String sql = "select * from user";
            preparedStatement = conn.prepareStatement(sql);
            ResultSet resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                String id = resultSet.getString(1);
                String name = resultSet.getString(2);
                Date time = resultSet.getDate(3);
                System.out.println(id + name + time);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

 18 代码查错

abstract class Name {
private String name;
public abstract boolean isStupidName(String name) {}
}
//错。abstract method必须以分号结尾，且不带花括号 
//public abstract boolean isStupidName(String name);

//**********************************************************
public class Something {
  void doSomething () {
  private String s = "";
  int l = s.length();
  }
}
//错。局部变量前不能放置任何访问修饰符 (private，public，和protected)。final可以用来修饰局部变量

//**********************************************************
abstract class Something {
private abstract String doSomething ();
}
//abstract的methods不能以private修饰。abstract的methods就是让子类implement(实现)具体细节。abstract method前也不能加final

//*********************************************************
public class Something {
public int addOne(final int x) {
return ++x;
}
}
//错。int x被修饰成final，意味着x不能在addOne method中被修改。

//**********************************************************
public class Something {
   public static void main(String[] args) {
     Other o = new Other();
     new Something().addOne(o);
   }
   public void addOne(final Other o) {
    o.i++;
   }
}
class Other {
public int i;
}
//正确。在addOne method中，参数o被修饰成final。如果在addOne method里我们修改了o的reference(比如: o = new Other();)，那么如同上例这题也是错的。但这里修改的是o的member vairable(成员变量)，而o的reference并没有改变
//引用不能改变但是引用中对象的内容可以改变

//**********************************************************
class Something {
  int i；//正确，默认为0
  final int i;//错误，final int i =0; final修饰的没有默认值
  public void doSomething() {
    System.out.println("i = "+ i);
   }
}

//*********************************************************
public class Something {
   public static void main(String[] args) {
     Something s = new Something();
     System.out.println("s.doSomething() returns " + doSomething());
   }
  public String doSomething() {
   return "Do something ...";
   }
}
//静态方法里不能调用非静态方法

//**********************************************************
interface A {
    int x = 0;
}

class B {
    int x = 1;
}

class C extends B implements A {
    public void pX() {
        System.out.println(x);//编译时报错
        //System.out.println(A.x);
        //System.out.println(super.x);
    }
    public static void main(String[] args) {
        new C().pX();
    }
}

//**********************************************************
interface Playable {
    void play();
}

interface Bounceable {
    void play();
}

interface Rollable extends Playable, Bounceable {
    Ball ball = new Ball("PingPang");//默认为public static final Ball ball = new Ball("PingPang");
}

class Ball implements Rollable {
    private String name;
    public String getName() {
        return name;
    }

    public Ball(String name) {
        this.name = name;
    }

    public void play() {
         ball = new Ball("Football");//final修饰的对象，引用是不能被改变的。所以报错
        System.out.println(ball.getName());
    }
}