java学习日记 反射机制

1、认识class类

1）产生了实例化对象

import java.util.Date;

public class GetClassDemo1 {
    public static void main(String[] args) {
        Date date = new Date();
        Class<?> cls = date.getClass();
        System.out.println(cls);
    }
}

2）未产生实例化对象

import java.util.Date;

public class GetClassDemo1 {
    public static void main(String[] args) {
        Class<?> cls = Date.class;
        System.out.println(cls);
    }
}

3）调用class类的方法，不用import语句导入明确的类，采用forname方法描述类名称。

public class GetClassDemo1 {
    public static void main(String[] args) throws ClassNotFoundException {
        Class<?> cls = Class.forName("java.util.Date");
        System.out.println(cls);
    }
}

运行结果相同：

class java.util.Date

 2、对象实例化

class BookObject{
    public BookObject(){
        System.out.println("***无参构造***");
    }

    @Override
    public String toString() {
        return "这是一个例子";
    }
}
public class GetClassDemo1 {
    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        Class<?> cls = Class.forName("com.hengqin.test1.BookObject");
        Object obj = cls.newInstance();
        System.out.println(obj);
    }
}

interface IFruit{
    public void eat();
}

class Appl implements IFruit{

    @Override
    public void eat() {
        System.out.println("***吃苹果***");
    }
}

class Factory2{
    public static IFruit getInstance(String classname){
        IFruit f = null;
        try {
            f = (IFruit) Class.forName(classname).newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return f;
    }
}
public class FactorRegexDemo1 {
    public static void main(String[] args) {
        IFruit f = Factory2.getInstance("com.hengqin.test1.Appl");
        f.eat();
    }
}

3、使用反射调用构造（明确调用类中的有参构造）

import java.lang.reflect.Constructor;

public class GetConstructDemo1 {
    public static void main(String[] args) throws Exception {
        Class<?> cls = Class.forName("com.hengqin.test1.Book");
        Constructor<?> con = cls.getConstructor(String.class,double.class);
        Object obj = con.newInstance("java",89.7);
        System.out.println(obj);
    }
}

4、反射调用方法

public class GetConstructDemo1 {
    public static void main(String[] args) throws Exception {
        String filename = "title";
        Class<?> cls = Class.forName("com.hengqin.test1.Book1");
        Object obj = cls.newInstance();
        Method setMet = cls.getMethod("set"+initcap(filename), String.class);
        Method getMet = cls.getMethod("get"+initcap(filename));
        setMet.invoke(obj,"java");
        System.out.println(getMet.invoke(obj));
    }
    public static String initcap(String str){
        return str.substring(0,1).toUpperCase()+str.substring(1);
    }
}