＜03.13＞八股文补充知识

 

 

 

 

 

 

 

 

 

 

import java.lang.reflect.*;
public class Main {

    public static void main(String[] args) throws Exception {
        // 获取 Class 对象
    	//1. 通过类字面量
    	Class<?> clazz = Person.class;
        //2 通过对象实例化
    	String str = "Hello";
    	Class<?> clazz_str = str.getClass();//将打印出clazz_str变量的值class java.lang.String
    	System.out.println(clazz_str);
    	//3 通过 Class.forName()方法
    	Class<?> clazz_for = Class.forName("java.lang.String");
    	System.out.println(clazz_for);
    	
        // 创建对象
    	//可以用反射动态创建对象
    	Class<?> clazz_create = Class.forName("java.lang.String");
    	Object obj = clazz_create.getDeclaredConstructor().newInstance();
    	System.out.println(obj);
    	
        Constructor<?> constructor = clazz.getConstructor(String.class, int.class);
        Object person = constructor.newInstance("John", 30);
        System.out.println(person);//打印出来的是地址
        
        // 访问字段
        Field nameField = clazz.getDeclaredField("name");
        nameField.setAccessible(true);
        System.out.println("Name: " + nameField.get(person));
        
        // 修改字段
        nameField.set(person, "Doe");
        System.out.println("Updated Name: " + nameField.get(person));
        
        // 调用方法
        Method greetMethod = clazz.getMethod("greet", String.class);
        greetMethod.invoke(person, "World");
    }
}

class Person {
    private String name;
    private int age;

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

    public void greet(String message) {
        System.out.println(name + " says: " + message);
    }
}

 

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

public class Main {

    public static void main(String[] args) throws Exception {
        // 获取 Class 对象
        Class<?> clazz = Car.class;

        // 创建 Car 对象
        Constructor<?> constructor = clazz.getConstructor(String.class, int.class);
        Object car = constructor.newInstance("Toyota", 2020);
        
        // 访问字段
        Field modelField = clazz.getDeclaredField("model");
        Field yearField = clazz.getDeclaredField("year");
        
        // 设置字段为可访问（如果字段是私有的）
        modelField.setAccessible(true);
        yearField.setAccessible(true);
        
        // 打印原始字段值
        System.out.println("Original Model: " + modelField.get(car));
        System.out.println("Original Year: " + yearField.get(car));
        
        // 修改字段值
        modelField.set(car, "Honda");
        yearField.set(car, 2024);
        
        // 打印修改后的字段值
        System.out.println("Updated Model: " + modelField.get(car));
        System.out.println("Updated Year: " + yearField.get(car));
        
        // 调用方法
        Method startMethod = clazz.getMethod("start");//start是方法名
        startMethod.invoke(car);
    }
}

class Car {
    private String model;
    private int year;

    public Car(String model, int year) {
        this.model = model;
        this.year = year;
    }

    public void start() {
        System.out.println("The " + model + " car of year " + year + " is starting.");
    }
}

 

 

 

 

 

import java.io.*;
 
public class SerializeDemo
{
   public static void main(String [] args)
   {
      Employee e = new Employee();
      e.name = "Reyan Ali";
      e.address = "Phokka Kuan, Ambehta Peer";
      e.SSN = 11122333;
      e.number = 101;
      try
      {
         FileOutputStream fileOut =
         new FileOutputStream("/tmp/employee.ser");
         ObjectOutputStream out = new ObjectOutputStream(fileOut);
         out.writeObject(e);
         out.close();
         fileOut.close();
         System.out.printf("Serialized data is saved in /tmp/employee.ser");
      }catch(IOException i)
      {
          i.printStackTrace();
      }
   }
}

import java.io.*;
 
public class DeserializeDemo
{
   public static void main(String [] args)
   {
      Employee e = null;
      try
      {
         FileInputStream fileIn = new FileInputStream("/tmp/employee.ser");
         ObjectInputStream in = new ObjectInputStream(fileIn);
         e = (Employee) in.readObject();
         in.close();
         fileIn.close();
      }catch(IOException i)
      {
         i.printStackTrace();
         return;
      }catch(ClassNotFoundException c)
      {
         System.out.println("Employee class not found");
         c.printStackTrace();
         return;
      }
      System.out.println("Deserialized Employee...");
      System.out.println("Name: " + e.name);
      System.out.println("Address: " + e.address);
      System.out.println("SSN: " + e.SSN);
      System.out.println("Number: " + e.number);
    }
}