Java反射

Java反射为开发者提供了更灵活的方式编程，可以在运行时操纵类的构造方法、属性和方法。

1、调用类的公有方法

Car类作为通过反射获取其isExpensive（）方法

package com.reflect;
public class Car {
 private String name;
 
 private Long price;
 
    public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public Long getPrice() {
  return price;
 }
 public void setPrice(Long price) {
  this.price = price;
 }
 public boolean isExpensive(Long price) {
        if(price>200000L){
         System.out.println("this car price is more than 20w!");
            return true;
        } else {
         System.out.println("this car price is less than 20w!");
            return false;
        }
    }
}

写一个方法进行反射调用

public class ReflectTest {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, InstantiationException {
        Class<?> myTest = Class.forName("com.discover.amazing.reflect.Car");
        Method fun1 = myTest.getMethod("isExpensive", Long.class);
        boolean result =  (Boolean) fun1.invoke(myTest.newInstance(), 500000L);
    }

}

2、操纵类的属性

修改Car类的isExpensive()方法

public class Car {
	private String name;
	
	private Long price;
	
    public String getName() {
		return name;
	}

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

	public Long getPrice() {
		return price;
	}

	public void setPrice(Long price) {
		this.price = price;
	}

	public boolean isExpensive() {
        if(this.getPrice()>200000L){
        	System.out.println("this car price is more than 20w!");
            return true;
        } else {
        	System.out.println("this car price is less than 20w!");
            return false;
        }
    }
}

通过反射获取类的属性，然后设置该属性的值

public class ReflectTest {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        Class<?> car = Class.forName("com.discover.amazing.reflect.Car");
        Method fun1 = car.getMethod("isExpensive");
        Field priceField = car.getDeclaredField("price");
        Object carInstance = car.newInstance();
        priceField.setAccessible(true);
        priceField.set(carInstance, 150000L);
        boolean result =  (Boolean) fun1.invoke(carInstance);
    }

}

3、操纵类的构造方法

在Car类中增加构造方法

public class Car {
	private String name;
	
	private Long price;
	
    public String getName() {
		return name;
	}

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

	public Long getPrice() {
		return price;
	}

	public void setPrice(Long price) {
		this.price = price;
	}
	
	public Car(String name, Long price) {
		this.name = name;
		this.price = price;
	}

	public boolean isExpensive() {
        if(this.getPrice()>200000L){
        	System.out.println("this car price is more than 20w!");
            return true;
        } else {
        	System.out.println("this car price is less than 20w!");
            return false;
        }
    }
}

通过反射获取构造方法，通过构造方法实例化一个Car对象，然后调用Car的 isExpensive()方法

public class ReflectTest {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        Class<?> clazz = Class.forName("com.discover.amazing.reflect.Car");
        Constructor<?> carConstructor = clazz.getDeclaredConstructor(String.class, Long.class);
        carConstructor.setAccessible(true);
        Car car = (Car) carConstructor.newInstance("Benz", 500000L);
        car.isExpensive();
    }

}