Java基础

--------------------------------------------------------泛型----------------------------------------------------------------------------------------------

package com.lvym.generic;

import java.util.ArrayList;
import java.util.Iterator;

/**
 * 
 */
public class GenericDemo {
    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();//默认类型Object 大小10
        arrayList.add(1);
        arrayList.add("dd");

        ArrayList<Integer> arrayList1 = new ArrayList<>();
        arrayList1.add(1);

        ArrayList<String> arrayList2 = new ArrayList();
        arrayList2.add("dd");
        select(arrayList1);

    }

  //泛型通配符只能接收数据不能存储数据
    public static void select(ArrayList<?> list) {
        Iterator<?> iterator = list.iterator();
        while (iterator.hasNext()) {
            Object next = iterator.next();
            System.out.println(next);
        }
    }

package com.lvym.generic;

/**
 * 需要声明泛型  否则报错
 * @param <T>
 */
public class Demo<T> {


    private Integer id;
    private T data;
}

-----------------------------------------------------------------------数组--------------------------------------------------------------------------------------------------------------------------------

查询快：数组的地址是连续的，通过首地址（在栈中）就可以找到数组，再通过索引就可以很快找到数据

增删慢：数组的长度是固定的，想要删除或增加元素就必须创建一个新数组(已经发生改变，已经增加或删除之后的，目标数组)，把原数组拷贝到新数组，原数组将被GC回收。

 

 

  -----------------------------------------------------------------------链表--------------------------------------------------------------------------------------------------------------------------------

 

 ----------------------------------------------------------------------------------------------------------------栈FILO        队列FIFO  ----------------------------------------------------------------------------------------------------

 

 

-------------------------------------------------------------------------------------------树-------------------------------------------------------------------------------------------------------------------------------

 --------------------------------------------------------------------------------------------哈希-----------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Map<String,String> map=new HashMap<>();
        String put = map.put("1", "1");
           String put2 = map.put("1", "2");
        System.out.println(put);//null  需要再添加才能打印

               System.out.println(put);//2

Map<String,String> map=new HashMap<>();
map.put("1","1");
System.out.println(map);//{1=1}

 Map<String,String> map=new HashMap<>();
        map.put("1","1");
        map.put("2","1");
        map.put("3","1");
        map.put("4","1");
        map.put("5","1");
        map.put("6","6");
//也可使用迭代器
        for (String s : map.keySet()) {

            System.out.println(map.get(s));
        }

 

 

 Map<String,String> map=new HashMap<>();
        map.put("1","1");
        map.put("2","1");
        map.put("3","1");
        map.put("4","1");
        map.put("5","1");
        map.put("6","6");

        Set<Map.Entry<String, String>> entrySet = map.entrySet();
        for (Map.Entry<String, String> stringStringEntry : entrySet) {
            System.out.println(stringStringEntry.getValue());
        }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 ---------------------------------------子类异常不能大于父类异常，所以抛父类异常也可以----------------------------------------

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

package com.lvym.generic;


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

    public static void main(String[] args) {

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.execute(()->{
            System.out.println(Thread.currentThread().getName());
        });
        executorService.execute(()->{
            System.out.println(Thread.currentThread().getName());
        });
        executorService.execute(()->{
            System.out.println(Thread.currentThread().getName());
        });
    }

}

结果：
pool-1-thread-1
pool-1-thread-2
pool-1-thread-2

 

 

 

 

  File file = new File("d:");//当前目录
        String[] list = file.list();
        for (String s : list) {
            System.out.println(s);
        }
        System.out.println("-------------------------------------");
        File file2 = new File("d://");//D盘根目录
        File[] files = file2.listFiles();
        for (File file1 : files) {
            System.out.println(file1);
        }

 

 

 

 

 

 

 

 

 

 

 

 

                  UTF-8：一个英文占一个字节

 

 

 

 

 

 

 

 

  不存在的文件会创建，      write方法会覆盖，

 

 

 

 

 

 

  try(   FileWriter fileWriter = new FileWriter("C:\\Users\\14829\\Desktop\\a.txt")) {
            fileWriter.write("n");
          
        }catch (Exception e){
            System.out.println(e);
        }

 

 

 

 

        Properties properties = new Properties();

        properties.setProperty("幂","lvym");
        properties.setProperty("幂1","lvym");
        properties.setProperty("幂2","lvym");

        Set<String> set = properties.stringPropertyNames();
        for (String s : set) {
            String property = properties.getProperty(s);
            System.out.println(property);
        }

 

 

 Properties properties = new Properties();

        properties.setProperty("幂","lvym");
        properties.setProperty("幂1","lvym");
        properties.setProperty("幂2","lvym");

       properties.store(new FileWriter("C:\\Users\\14829\\Desktop\\a.txt"),"");
   //properties.store(new FileOutputStream("C:\\Users\\14829\\Desktop\\a.txt"),"");

 

 

 Properties properties = new Properties();

        properties.load(new FileReader("C:\\Users\\14829\\Desktop\\a.txt"));
        //properties.load(new FileInputStream("C:\\Users\\14829\\Desktop\\a.txt"));
        Set<String> set = properties.stringPropertyNames();
        for (String s : set) {
            System.out.println(properties.getProperty(s));

        }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

package com.lvym.generic;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

public class TcpClient {
    public static void main(String[] args) throws IOException {
        //创建客户端对象
        Socket socket = new Socket("127.0.0.1", 8888);
        //使用Socket对象中的方法getOutputStream()获取网络字节输出流
        OutputStream outputStream = socket.getOutputStream();
        //向服务器发送数据
        outputStream.write("Hello,服务器".getBytes());
        //利用Socket获得输入流读取
        InputStream inputStream = socket.getInputStream();
        byte[] bytes = new byte[1024*1];
        int len= inputStream.read(bytes);
        System.out.println(new String(bytes,0,len));
        //关闭链接
        socket.close();

    }
}

 

 

 

 

 

 

package com.lvym.generic;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServer {
    public static void main(String[] args) throws IOException {
        //创建服务器
        ServerSocket serverSocket = new ServerSocket(8888);
        //使用serverSocket.accept();获得Socket
        Socket accept = serverSocket.accept();
         //利用Socket获得输入流读取
        InputStream inputStream = accept.getInputStream();
        byte[] bytes = new byte[1024];
        int len= inputStream.read(bytes);
        System.out.println(new String(bytes,0,len));
        //利用Socket获得输出流
        OutputStream outputStream = accept.getOutputStream();
        outputStream.write("收到".getBytes());
        //释放资源
        accept.close();
        serverSocket.close();




    }
}

 

 

  /**
     *     只有单列集合才能转流
     * @param args
     */
    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        Stream<String> stream = list.stream();

        Set<Integer> set=new HashSet<>();
        Stream<Integer> stream1 = set.stream();

        Map<String,Integer> map=new HashMap<>();
        Set<String> keySet = map.keySet();
        Stream<String> stream2 = keySet.stream();

        Collection<Integer> values = map.values();
        Stream<Integer> stream3 = values.stream();

        Set<Map.Entry<String, Integer>> entries = map.entrySet();
        Stream<Map.Entry<String, Integer>> stream4 = entries.stream();


        Stream<Integer> stream5 = Stream.of(1, 2, 3, 4, 5);

        int[] a={1,2,3};
        Stream<int[]> a1 = Stream.of(a);

        Integer[] b={1,2,3};
        Stream<Integer> b1 = Stream.of(b);
        
        String[] c={"a","b"};
        Stream<String> c1 = Stream.of(c);
        

    }

静态方法不可以调用非静态，非静态可以调用静态

 

 

 

 

 

        Class<?> aClass = Class.forName("com.lvym.generic.Person");
        System.out.println(aClass);
        
        Class personClass = Person.class;
        System.out.println(personClass);

        Class aClass1 = new Person().getClass();
        System.out.println(aClass1); 

 

 

 

package com.lvym.generic;

public class Person {
    private String name;
    private Integer age;

    public String a;
    protected String b;
     String c;
    private Integer d;

    public Person() {
    }


    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;

    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    public String getA() {
        return a;
    }

    public void setA(String a) {
        this.a = a;
    }

    public String getB() {
        return b;
    }

    public void setB(String b) {
        this.b = b;
    }

    public String getC() {
        return c;
    }

    public void setC(String c) {
        this.c = c;
    }

    public Integer getD() {
        return d;
    }

    public void setD(Integer d) {
        this.d = d;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", a='" + a + '\'' +
                ", b='" + b + '\'' +
                ", c='" + c + '\'' +
                ", d=" + d +
                '}';
    }
}

package com.lvym.generic;


import java.lang.reflect.Field;

public class Test {

    public static void main(String[] args) throws Exception {

       //获取反射类
        Class personClass = Person.class;
        //Class<Person> personClass = Person.class;

        Field[] fields = personClass.getFields();//获取public修饰的成员变量
        for (Field field : fields) {
            System.out.println(field);
        }

        Field a = personClass.getField("a");//获取指定成员变量
        Person person = new Person();
        Object o = a.get(person);//获取a的值
        System.out.println(o);

        a.set(person,"幂");//设置a的值
        System.out.println(person);

        Field[] declaredFields = personClass.getDeclaredFields();//获取所有的成员变量，不区分修饰符
        for (Field declaredField : declaredFields) {
            System.out.println(declaredField);
        }
        Field field = personClass.getDeclaredField("d");//获取指定成员变量  不区分修饰符
        field.setAccessible(true);//忽略权限检查 否则获取private修饰的报错java.lang.IllegalAccessException
        Object o1 = field.get(person);
        System.out.println(o1);

        field.set(person,12);//设置值   也需要忽略权限检查
        System.out.println(person);

    }

}

...

    private Person() {
    }


    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;

    }
....

   //获取反射类
        Class personClass = Person.class;
        //Class<Person> personClass = Person.class;

        Constructor constructor = personClass.getConstructor(String.class,Integer.class);//获取有参构造器
        Person p = (Person) constructor.newInstance("幂", 18);//创建对象
        System.out.println(p);

       /* Constructor constructor1 = personClass.getConstructor();//获取空参构造器,不能获取private，会报错
        Object o = constructor1.newInstance();//创建对象
        System.out.println(o);
        Object o1 = personClass.newInstance();//创建对象
        System.out.println(o1);*/

        Constructor[] constructors = personClass.getConstructors();//获取所有构造器,不能获取private ，不会报错
        for (Constructor constructor2 : constructors) {
            System.out.println(constructor2);
        }

        Constructor[] declaredConstructors = personClass.getDeclaredConstructors();//获取所有构造器，不区分构造器
        for (Constructor declaredConstructor : declaredConstructors) {
            System.out.println(declaredConstructor);
        }

        Constructor declaredConstructor = personClass.getDeclaredConstructor(String.class,Integer.class);//获取指定构造器，不区分构造器
     //   declaredConstructor.setAccessible(true);//忽略权限检查
        Object o = declaredConstructor.newInstance("幂", 18);//创建对象
        System.out.println(o);

 

... 
 public void aVoid(){
        System.out.println("aVoid");
    }
     void bVoid(){
        System.out.println("bVoid");
    }
    protected void cVoid(){
        System.out.println("cVoid");
    }
    public void aVoid(int in){
        System.out.println("aVoid "+in);
    }
    private void eVoid(){
        System.out.println("eVoid");
    }
...

 //获取反射类
        Class personClass = Person.class;
        //Class<Person> personClass = Person.class;

        Method aVoid = personClass.getMethod("aVoid",int.class);//获取public修饰有参方法
        Person person = new Person();
        aVoid.invoke(person,10);
        Method aVoid2 = personClass.getMethod("aVoid");//获取public修饰无参方法
        aVoid2.invoke(person);

        Method[] methods = personClass.getMethods();//获取所有public修饰方法
        for (Method method : methods) {
            System.out.println(method);
            String name = method.getName();
            System.out.println(name);
        }

        Method eVoid = personClass.getDeclaredMethod("eVoid");//获取指定方法   不区分修饰符
        eVoid.setAccessible(true);//忽略权限检查
        eVoid.invoke(person);

        Method[] declaredMethods = personClass.getDeclaredMethods();//获取所有方法
        for (Method declaredMethod : declaredMethods) {
            System.out.println(declaredMethod);
            String name = declaredMethod.getName();
            System.out.println(name);
        }

-----------------------------------------------反射实例--------------------------------------------

 

 

       //通过修改配置文件，改变运行的方法
        Properties properties = new Properties();//创建Properties集合对象 唯一与IO相结合的集合对象
        ClassLoader classLoader = Test.class.getClassLoader();//把Test类加载进内存，借助类加载器找到pro.properties文件
        InputStream resourceAsStream = classLoader.getResourceAsStream("pro.properties");
        properties.load(resourceAsStream);//把pro.properties加载进集合，以供使用

        String className = properties.getProperty("className");//读取 className值
        String methodName = properties.getProperty("methodName");//读取 methodName值

        Class<?> aClass = Class.forName(className);//把类加载进内存
        Object o = aClass.newInstance();//创建对象
        Method method = aClass.getMethod(methodName);//获得方法
        method.invoke(o);//执行方法

 

 

 

 

 

 

 

 

 

 

 ------------------------------------例子------------------------------------------------------------

package com.lvym.generic;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
    String className();
    String methodName();
}

package com.lvym.generic;

import java.lang.reflect.Method;


@MyAnnotation(className = "com.lvym.generic.Person",methodName = "aVoid")
public class Test {

    public static void main(String[] args) throws Exception {

         //解析注解
        Class<Test> testClass = Test.class;//获得类的字节码文件

        MyAnnotation annotation = testClass.getAnnotation(MyAnnotation.class);//获得注解类   本质就是在内存生成该注解接口的实现类

        String className = annotation.className();//获得类
        String methodName = annotation.methodName();//获得方法


        Class<?> aClass = Class.forName(className);//把类加载进内存
        Object o = aClass.newInstance();//创建对象
        Method method = aClass.getMethod(methodName);//获得方法
        method.invoke(o);//执行方法


    }

}