java高级篇

Method对象可以得到任何一个类的任何方法的定义（只需要传入方法的名字和参数即可）

class Ming {
    private void speak() {
        System.out.println("ff");
    }
}

public class Main {
    public static void main(String[] args) throws NoSuchMethodException {
        Method method = Ming.class.getDeclaredMethod("speak");
        System.out.println(method.toString());
    }
}
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有参数的话，需要int.class

class Ming {
    void speak(int a) {
        System.out.println("ff");
    }
}

public class Main {
    public static void main(String[] args) throws NoSuchMethodException {
        Ming s = new Ming();
        Method method = s.getClass().getDeclaredMethod("speak", int.class);
        System.out.println(method);
    }
}
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输出   private void Ming.speak() 

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

得到类的构造函数

getConstructor只能得到public的

import java.lang.reflect.Constructor;

class Second {
    int a, b;
    public Second() {
        a = b = 1;
    }
    Second(int _a, int _b) {
        a = _a;
        b = _b;
    }
    void show() {
        System.out.println(a + b);
    }
};
public class Main {
    public static void main(String[] args) throws InterruptedException, NoSuchMethodException, SecurityException {
        Second second = new Second();
        System.out.println(second.toString());
        System.out.println(second.getClass().getConstructor().toString());
        // getConstructor只能用在public 的构造方法
        
        
        /*  输出 
            Second@7852e922
            public Second()
        */
    }
}
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getDeclaredConstructor可以得到所有的

import java.lang.reflect.Constructor;

class Second {
    int a, b;
    public Second() {
        a = b = 1;
    }
    Second(int _a, int _b) {
        a = _a;
        b = _b;
    }
    void show() {
        System.out.println(a + b);
    }
};
public class Main {
    public static void main(String[] args) throws InterruptedException, NoSuchMethodException, SecurityException {
        Second second = new Second();
        System.out.println(second.toString());
        System.out.println(second.getClass().getDeclaredConstructor(int.class, int.class).toString());
        // getConstructor只能用在public 的构造方法
        
        
        /*  输出 
            Second@7852e922
            Second(int,int)
        */
    }
}
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-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

getField得到的是变量名

import java.lang.reflect.Field;
import java.lang.reflect.Method;

class Ming {
    private void speak() {
        System.out.println("ff");
    }
    public int vb;
    public int a;
    public Ming() {}
}

public class Main {
    public static void main(String[] args) throws NoSuchMethodException {
        Ming ming = new Ming();
        Field[] fields = ming.getClass().getFields();
        for (Field field : fields) {
            System.out.println(field.toString());
        }
        //public int Ming.vb
        //public int Ming.a
    }
}
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可以得到单个的，传入名字就可以

import java.lang.reflect.Field;
import java.lang.reflect.Method;

class Ming {
    private void speak() {
        System.out.println("ff");
    }
    private int vb;
    public int a;
    public Ming() {}
}

public class Main {
    public static void main(String[] args) throws Exception {
        Ming ming = new Ming();
        Field field = ming.getClass().getDeclaredField("vb");
        System.out.println(field.toString());
        
    }
}
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抛出异常，绝招，直接throw Expection即可，不用throw XXXExpection

反射机制，大概就是得到名字，就可以得到所有东西，可以修改属性。

得到一个类的名字，可以用forname方法生成他的一个对象。

然后，可以用getField得到它的一个属性，也就是变量。

然后用Field.set(对象名， val)就可以修改成功。也可以修改private的变量。超劲。

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.math.BigInteger;
import java.util.Scanner;

class Ming {
    private int a;
    Ming() {
        
    }
    void speak() {
        System.out.println("fff");
    }
    int show() {
        return a;
    }
}

public class Main {
    public static void main(String[] args) throws Exception { // 666
        Class clazz = Class.forName("Ming");
        Ming s = (Ming)clazz.newInstance();
        Field field = clazz.getDeclaredField("a");
        field.setAccessible(true); //修改private
        field.set(s, 20);
        System.out.println(s.show());
    }
}
View Code
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.math.BigInteger;
import java.util.Scanner;

class Ming {
    private int a;
    Ming() {
        
    }
    void speak() {
        System.out.println("fff");
    }
    int show() {
        return a;
    }
}

public class Main {
    public static void main(String[] args) throws Exception { // 666
        Class clazz = Class.forName(Ming.class.getName()); //这样来
        Ming s = (Ming)clazz.newInstance();
        Field field = clazz.getDeclaredField("a");
        field.setAccessible(true); //修改private
        field.set(s, 20);
        System.out.println(s.show());
    }
}
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利用java反射得到一个类的所有东西，不能得到方法实现的内容

import java.io.File;
import java.io.PrintWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Scanner;

class Person {
    private String name, sex, idNo;
    Integer age;
    Boolean isMerried;
    int a;

    public String getName() {
        return name;
    }

    public String getSex() {
        return sex;
    }

    public String getIdNo() {
        return idNo;
    }

    public Integer getAge() {
        return age;
    }

    public Boolean getIsMerried() {
        return isMerried;
    }

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

    public void setSex(String sex) {
        this.sex = sex;
    }

    public void setIdNo(String idNo) {
        this.idNo = idNo;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public void setIsMerried(Boolean isMerried) {
        this.isMerried = isMerried;
    }

    private void show(int a, int b, char c, int d) {
    }

    public Person() {
    }

    public Person(String idNo) {
        this.idNo = idNo;
    }

    public Person(String idNo, Integer fuck) {
    }

    public String toString() {
        return name + "  " + sex + " " + age + " " + idNo + " " + isMerried; // 需要两个空格？，因为中文，靠
    }
}

class PersonProxy {
    private Person T;
    private final String OUTPUT = "output.txt";
    private PrintWriter output = new PrintWriter(OUTPUT);

    PersonProxy(Person T) {
        this.T = T;
    }

    private void writeFile(String message) {

    }
}

public class Main {
    static private final String INPUT = "input.txt";
    static private final String OUTPUT = "output.txt";
    static private final String CMP = "java.lang.";
    static private final int MAXN = 200;
    
    static private int[] del = new int[MAXN];
    static private int DFN = 0;
    
    private static String getString(String str, String className) {
        ++DFN;
        for (int j = 0; j < str.length(); ++j) {
            if (del[j] == DFN)
                continue;
            String t = "";
            if (j + 10 < str.length()) {
                t = str.substring(j, j + 10);
                if (t.compareTo(CMP) == 0) {
                    for (int k = j; k < j + 10; ++k)
                        del[k] = DFN;
                }
            }
            if (j + className.length() + 1 < str.toString().length()) {
                t = str.substring(j, j + className.length() + 1);
                if (t.compareTo(className + ".") == 0) {
                    for (int k = j; k < j + className.length() + 1; ++k)
                        del[k] = DFN;
                }
            }
        }

        String out = "	";
        for (int j = 0; j < str.length(); ++j) {
            if (del[j] == DFN)
                continue;
            out += str.charAt(j);
        }
        return out + ";";
    }

    private static void showClassInformation(String className) throws Exception {
        System.out.println("class" + " " + className + " {");
        Class clazz = Class.forName(className);
        Field[] fs = clazz.getDeclaredFields();
        for (Field i : fs) {
            System.out.println(getString(i.toString(), className));
        }
        Constructor[] cs = clazz.getDeclaredConstructors();
        for (Constructor i : cs) {
            System.out.println(getString(i.toString(), className));
        }
        Method[] ms = clazz.getDeclaredMethods();
        for (Method i : ms) {
            System.out.println(getString(i.toString(), className));
        }
        System.out.println("}");
    }

    public static void getInstance(String className) throws Exception {
        Class clazz = Class.forName(className);
        Person ps = (Person) clazz.newInstance();
        ps.setIdNo("5122245566");
        ps.setName("张小平");
        ps.setAge(23);
        ps.setSex("Male");
        ps.setIsMerried(true);
        PrintWriter output = new PrintWriter(OUTPUT);
        output.println("idNo=" + ps.getIdNo());
        output.println("name=" + ps.getName());
        output.println("age=" + ps.getAge());
        output.println("sex=" + ps.getSex());
        output.println("isMerried=" + ps.getIsMerried());
        output.close();
    }

    public static void getFile(String className) throws Exception {
        Class clazz = Class.forName(className);
        Person ps = (Person) clazz.newInstance();
        Scanner input = new Scanner(new File(INPUT));
        String str;
        str = input.next();
        ps.setIdNo(str.substring(str.lastIndexOf('=') + 1, str.length()));
        str = input.next();
        ps.setName(str.substring(str.lastIndexOf('=') + 1, str.length()));
        str = input.next();
        ps.setAge(Integer.parseInt(str.substring(str.lastIndexOf('=') + 1, str.length())));
        str = input.next();
        ps.setSex(str.substring(str.lastIndexOf('=') + 1, str.length()));
        str = input.next();
        ps.setIsMerried(Boolean.parseBoolean(str.substring(str.lastIndexOf('=') + 1, str.length())));

        System.out.println(ps.toString());
        input.close();
    }

    
    public static void main(String[] args) throws Exception {
        showClassInformation("Person");
        getInstance("Person");
        getFile("Person");
    }
}
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文件追加操作

    public void writeFile(String methodName, String parm) throws IOException {
        output = new PrintWriter(new FileWriter(new File(OUTPUT), true)); // 文件追加
        String message = "时间: " + getNowTime() + " 方法名称: " + methodName + " 参数" + parm;
        output.println(message);
        output.close();
    }

利用动态代理，需要的是设计一个接口，里面写了什么，就能代理出来。

public interface Speakable {
    public void speak(String message);
    public String getName();
    public String getSex();
    public String getIdNo();
    public Integer getAge();

    public Boolean getIsMerried();

    public void setName(String name);

    public void setSex(String sex);

    public void setIdNo(String idNo);

    public void setAge(Integer age);
    public void setIsMerried(Boolean isMerried);
}

写一个这样的接口，必须只能是接口

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyProxy implements InvocationHandler {
    private Object proxied;
    MyProxy(Object proxied) {
        this.proxied = proxied;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        method.invoke(this.proxied, args);
        System.out.println(PersonProxy.getNowTime()); //这一条就是
        return null;
    }
}

加上一条语句，就是每执行接口中的一个方法的时候，下面那句语句就能执行。所以就不需要在类中为每一个方法都写一句一毛一样的

        Person person = new Person();
        Speakable speakable = (Speakable)Proxy.newProxyInstance(Speakable.class.getClassLoader(), new Class[] {Speakable.class}, new MyProxy(person));
        speakable.setAge(2); //会输出时间
        System.out.println(person.getAge()); //不会输出时间

然后这样，每调用接口的一个方法，都会输出当前的时间。

这样做的好处就是，把一个对象，弄了一个代理给他，这样，那个代理做的东西，会直接影响那个对象的值，并且能够多输出一些你想要的东西。

Map的使用方法（假）

需要注意要判断后才能使用

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

import org.omg.PortableInterceptor.INACTIVE;
class Student {
    private String idNo, name;
    private int score;
    public Student(String idNo, String name, int score) {
        super();
        this.idNo = idNo;
        this.name = name;
        this.score = score;
    }
    public String getIdNo() {
        return idNo;
    }
    public void setIdNo(String idNo) {
        this.idNo = idNo;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    
}
class Score {
    private String course;
    private int score;
    public Score(String course, int score) {
        super();
        this.course = course;
        this.score = score;
    }
    public String getCourse() {
        return course;
    }
    public void setCourse(String course) {
        this.course = course;
    }
    public int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    
}
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        ArrayList<Student> st = new ArrayList<Student>();
        ArrayList<Score> sc = new ArrayList<Score>();
        Map<String, Integer> sumOfStudentScore = new HashMap<String, Integer>();
        Map<String, Integer> numberOfStudentSelect = new HashMap<String, Integer>();
        Map<String, Integer> mx = new HashMap<String, Integer>();
        Map<String, Integer> mi = new HashMap<String, Integer>();
        while (true) {
            System.out.println("请输入学生的学号、姓名、选修课程、课程成绩（学号是小数点结束输入）");
            String idNo = input.next();
            if (idNo.compareTo(".") == 0) break;
            String studentName = input.next();
            String courseName = input.next();
            int courseScore = input.nextInt();
            
            st.add(new Student(idNo, studentName, courseScore));
            sc.add(new Score(courseName, courseScore));
            
        }
        for (int i = 0; i < sc.size(); ++i) {
            String t = sc.get(i).getCourse();
            int val = sc.get(i).getScore();
            if (sumOfStudentScore.containsKey(t)) {
                int res = sumOfStudentScore.get(t) + val;
                sumOfStudentScore.put(t,  res);
                res = numberOfStudentSelect.get(t) + 1;
                numberOfStudentSelect.put(t, res);
                
                res = mx.get(t);  // 需要判断了才能使用
                mx.put(t, Math.max(res, val));
                res = mi.get(t);
                mi.put(t, Math.min(res, val));
            } else {
                sumOfStudentScore.put(t, val);
                numberOfStudentSelect.put(t, 1);
                mx.put(t, val);
                mi.put(t, val);
            }
        }
//        System.out.println("fff");
//        for (String s : sumOfStudentScore.keySet()) {
//            System.out.println(s + " " + sumOfStudentScore.get(s));
//        }
        for (String s : sumOfStudentScore.keySet()) {
            System.out.println("课程: " + s + " 平均分是：" + sumOfStudentScore.get(s) * 1.0 / numberOfStudentSelect.get(s));
            System.out.println("其中最高分是:" + mx.get(s) + "  " + "最低分是：" + mi.get(s));
        }
        String idNo;
        System.out.println("请输入想要查询的学生成绩的id");
        idNo = input.next();
        for (int i = 0; i < st.size(); ++i) {
            if (st.get(i).getIdNo().compareTo(idNo) == 0) {
                System.out.println(st.get(i).getScore());
            }
        }
    }
}
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泛型的使用方法

 
public class Main {
    public static void main(String[] args) {
        PersonManager<Student> ps = new PersonManager<Student>();
        ps.add(new Student("2015", "liuweiming"));
        ps.add(new Student("2014", "liuhaha"));
        ps.findAll();
    }
}



public class Person {
    String idNo, name;
}


import java.util.*;
public class PersonManager<T extends Person> {
    List<T> list;
    public PersonManager () {
        // TODO Auto-generated method stub
//        System.out.println("fff");
        list = new ArrayList<T>();
    }
    
//    public PersonManager<T> () {
//        
//    }

    public boolean add(T t) {
        if (list.contains(t)) return false;
        list.add(t);
        return true;
    }
    public boolean remove(T t) {
        if (!list.contains(t)) return false;
        list.remove(t);
        return true;
    }
    public T findById(int id) {
        for (T i : list) {
            if (i.getClass().isInstance(Student.class)) {
                if (((Student)i).getIdNo().compareTo("" + id) == 0) {
                    return i;
                }
            } else {
                if (((Teacher)i).getIdNo().compareTo("" + id) == 0) {
                    return i;
                }
            }
        }
        return list.get(0); //  wrong answer, 
    }
    public void findAll() {
        for (T i : list) {
            System.out.println(i.toString());
        }
    }
}



public class Student extends Person {
    String idNo, name;

    public String getIdNo() {
        return idNo;
    }

    public void setIdNo(String idNo) {
        this.idNo = idNo;
    }

    public String getName() {
        return name;
    }

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

    public Student(String idNo, String name) {
        super();
        this.idNo = idNo;
        this.name = name;
    }
    @Override
    public String toString() {
        return idNo + " " + name;
    }
}



public class Teacher extends Person {
    String idNo, name;

    public String getIdNo() {
        return idNo;
    }

    public void setIdNo(String idNo) {
        this.idNo = idNo;
    }

    public String getName() {
        return name;
    }

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

    public Teacher(String idNo, String name) {
        super();
        this.idNo = idNo;
        this.name = name;
    }
    @Override
    public String toString() {
        return idNo + " " + name;
    }
}
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2017年12月28日 20:30:05

坑：

如果一个方法里面有了 throws了东西，那么调用这个方法的时候就要try catch，或者在调用这个方法中的那个方法里面也throws东西。

还有，要注意左边红色的错误啊。。。。

java的web，服务器开了888端口，然后客户端要访问的也就是888端口。localhost就是127.0.0.1，不能写其他地址。写其他地址相当于访问别人的电脑了。

那个getport，随机化的，不能setport啊。 socket.getPort()

package liuweiming;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.*;

import javax.sound.sampled.Port;

class SocketHandler implements Runnable {
    private Socket socket;
    public SocketHandler(Socket socket) {
        this.socket = socket;
        // TODO Auto-generated constructor stub
    }
    public void run() {
        try {
            InputStreamReader inputStreamReader = new InputStreamReader(socket.getInputStream());
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String name = socket.getInetAddress().toString();
            name += ":";
            name += socket.getPort();
            System.out.println(name + " Say: " + bufferedReader.readLine());
            bufferedReader.close();
            inputStreamReader.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }
}

class ServerThread implements Runnable {
    
    public ServerThread() {
        
    }
    public void run() {
        try {
            ServerSocket serverSocket = new ServerSocket(888);
            while (true) {
                Socket socket = serverSocket.accept(); // 等待接受
                Thread thread = new Thread(new SocketHandler(socket));
                thread.start();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }
}

class Client {
    String inetAddress;
    int port;
    String fuck;
    public Client(String inetAddress, int port, String fuck) {
        this.inetAddress = inetAddress;
        this.port = port;
        this.fuck = fuck;
    }
    public void did() {
        Socket socket;
        try {
            socket = new Socket(inetAddress, port);
            
            PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
            printWriter.write(fuck);
            printWriter.flush();
            printWriter.close();
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Thread serverThread = new Thread(new ServerThread()); // 开启服务
        serverThread.start();
        
        Client client = new Client("127.0.0.1", 888, "df");
        client.did();
        Client client2 = new Client("127.0.0.1", 888, "fff");
        client2.did();
    }
}
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这次直接用浏览器做客户端，注意要加上一些话语才能show到去网页上。还有不知为何输出了两次（本地）

感觉访问了两次一样因为那个socket.getPort()不同的。

package liuweiming;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.*;

import javax.sound.sampled.Port;

class Sever {
    public void work() {
        try {
            ServerSocket serverSocket = new ServerSocket(8888); //监听这个端口
            while (true) { //一直accept
                Socket socket = serverSocket.accept();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String string = bufferedReader.readLine();
                PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
                System.out.println(socket.getInetAddress().toString() + "  " + socket.getPort() + " " + string);
                
                /*MK*/
                printWriter.println("HTTP/1.1 200 OK");
                printWriter.println("Content-Type: text/html;charset=UTF-8");
                printWriter.println();
                /*Mk*/
                
                printWriter.println("<p> fff </p>");
                printWriter.flush();    
                bufferedReader.close();
                printWriter.close();
                socket.close();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        
    }
}

public class Main {
    public static void main(String[] args) {
        Sever sever = new Sever();
        sever.work();
        
    }
}
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算法复杂度分析，大O阶、小O，Ω、.....

2018年1月3日 22:03:03

如果TomCat不能用

就在那个setclasspath.bat上，

加上那两个即可

如果想看看那个startup.bat为什么不行，可以在最后，也就是end；后面加上PAUSE让它停止。

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原文地址：https://www.cnblogs.com/liuweimingcprogram/p/7739943.html