＜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.StringSystem.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);}
}