2021.09.29

• 资源绑定器和类加载器：
• 可变长参数以及通过反射机制调用对象方法：
• 牛客网专项练习01：多态，线程安全，后台线程
• 牛客网专项练习02：线程抢占时间片，多态，值传递，包装类
• 自定义注解以及反射注解：
• 注解在开发中有什么用呢：注解经典案例

package du;

import java.util.ResourceBundle;

public class d819 {
    public static void main(String[] args) {
        
        ResourceBundle bundle = ResourceBundle.getBundle("du/classinfo");

        String className = bundle.getString("className");
        System.out.println(className); // 得到里面的东西 du/Product

        
    }
}

package du;

import java.lang.reflect.Method;

public class d827 {
    public static void main(String[] args) throws Exception{
        
        m1("123","abc","456","def");
        
        Class aClass = Class.forName("du.UserService");
        Object o = aClass.newInstance();
        
        Method aClassDeclaredMethodm2 = aClass.getDeclaredMethod("m2", String.class);
        
        Object hello_world = aClassDeclaredMethodm2.invoke(o, "hello world");
        System.out.println(hello_world); // null;
    }

    public static void m1(String... args){
        for (int i = 0; i < args.length; i++) {
            System.out.println(args[i]);
        }
    }
}

package du;

public class d999 {
    public static void main(String[] args) {
        
        byte y = 10;
        // byte x = y + y;

        
        // String string = new Object();

        

        
    }
}

package du;

import java.lang.annotation.Target;
import java.util.ArrayList;
import java.util.List;
import java.util.Date;

public class d999 {
    public static void main(String[] args) {
        
        
        PassO p = new PassO();
        p.start();

        
        base base = new Son();
        base.method();
        // base.methodB(); // 编译不通过

        
        new SuperTest().test();
        
        base1 base1 = new Derived();
        base1.methodOne();

        
        final NameList sl = new NameList();
        for (int i = 0; i < 2; i++) {
            new Thread(){
                public void run() {
                    sl.add("A");
                    sl.add("B");
                    sl.add("C");
                    sl.printAll();
                }
            }.start();
        }
    }
}


class Two {
    
    Byte x;
}

class PassO {
    
    void start() {
        Two t = new Two();
        System.out.print(t.x + ""); // null
        Two t2 = fix(t);
        System.out.print(t.x + " " + t2.x); // 42 42
    }

    Two fix(Two tt) {
        
        tt.x = 42;
        return tt;
    }
}


class base {
    
    public void method() {
        System.out.println("base");
    }
}

class Son extends base {
    public void method() {
        System.out.println("Son");
    }

    public void methodB() {
        System.out.println("SonB"); // 编译时出错
    }
    
}


class SuperTest extends Date {
    private static final long serialVersionUID = 1L;

    public void test() {
        
        System.out.println(super.getClass().getName()); // test.SuperClass
    }
}


class base1 {
    
    public void methodOne() {
        System.out.print("A"); // 1
        methodTwo(); // 调用子类的methodTwo
    }

    public void methodTwo() {
        System.out.print("B"); // 2
    }
}

class Derived extends base1 {
    public void methodOne() {
        super.methodOne(); // 调用父类的methodOne
        System.out.print("C"); // 4
    }

    public void methodTwo() {
        super.methodTwo(); // 调用父类的methodTwo
        System.out.print("D"); // 3
    }
}


class NameList {
    private List names = new ArrayList();

    synchronized void add(String name) {
        names.add(name);
    }
    
    synchronized void printAll() {
        for (int i = 0; i < names.size(); i++) {
            System.out.print(names.get(i) + "");
        }
    }
}

// MyAnnotation.java
package du;

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

@Target({ElementType.TYPE,ElementType.METHOD,ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
    
    String value() default "value";
    
    String information();
}

package du;
@MyAnnotation(information = "I am Tom cat")
public class d842 {
    private boolean flag;

    public static void main(String[] args) throws ClassNotFoundException{
        Class aClass = Class.forName("du.d842");
        
        // System.out.println(aClass.isAnnotationPresent(MyAnnotation.class));
        if (aClass.isAnnotationPresent(MyAnnotation.class)){
            
            MyAnnotation annotation = aClass.getAnnotation(MyAnnotation.class);
            System.out.println(annotation);
            
            System.out.println(annotation.information());
            
        }
    }
}

// Id.java
package du;

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 Id {}

// IdPropertyNotFoundException.java
package du;

public class IdPropertyNotFoundException extends RuntimeException{
    public IdPropertyNotFoundException(){}
    public IdPropertyNotFoundException(String string){
        super(string);
    }
}

package du;

import java.lang.reflect.Field;

@Id
public class d844 {

    // int id;
    String information;
    String methods;

    public static void main(String[] args) throws ClassNotFoundException{
        
        
        Class aClass = Class.forName("du.d844");
        if (aClass.isAnnotationPresent(Id.class)){
            
            Field[] declaredFields = aClass.getDeclaredFields();
            boolean haveIntId = false;
            for (Field declaredField : declaredFields) {
                if ("id".equals(declaredField.getName()) && "int".equals(declaredField.getType().getSimpleName())){
                    
                    haveIntId = true;
                    break;
                }
            }
            if (!haveIntId){
                throw new IdPropertyNotFoundException("Annotation @Id must have int type property id");
            }
        }
    }
    
}