【反射之Field】获取字段

 ■getFields()、getDeclaredFields()、getField() 和 getDeclaredField()的用法

package reflect.field;

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

public class FieldMethod {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        Class<?> personClass = Class.forName("reflect.Person");
        
        Constructor<?> constructor = personClass.getDeclaredConstructor(String.class, int.class, double.class, String.class);
        Object p = constructor.newInstance("周娟娟", 23, 80, "14计科1班");
        System.out.println(p.toString());
        
        
        // 该方法只能获取到公有的字段(属性)
        Field[] fields = personClass.getFields();
        for (Field field : fields) {
//            System.out.println(field);
        }
        
        // 该方法能获取到公有的、私有的、受保护的字段
        Field[] declaredFields = personClass.getDeclaredFields();
        for (Field field : declaredFields) {
//            System.out.println(field);
        }
        
        // 该方法只能获取到公有的字段，若传入的是私有或受保护的则会报错NoSuchFieldException
        Field nameFieldPublic = personClass.getField("className");
        
        nameFieldPublic.set(p, "卓越班");
        Method getClassName = personClass.getMethod("getClassName");
        Object className = getClassName.invoke(p);
        System.out.println(className);
        
        // 该方法可以获取到公有的、私有的、受保护的属性
        Field nameFieldPrivate = personClass.getDeclaredField("name");
        
        nameFieldPrivate.setAccessible(true);
//        System.out.println(nameFieldPrivate);
        nameFieldPrivate.set(p, "Jay");
        System.out.println(p);
        
        // 获取到私有属性age
        Field ageFieldPrivate = personClass.getDeclaredField("age");
        // 忽略修饰符访问检查
        ageFieldPrivate.setAccessible(true);
        // 设置age的值，必须指明修改的是哪个对象的属性
        ageFieldPrivate.set(p, 24);
        System.out.println(p);
        
    }

}

package reflect;

public class Person {
    
    private String name;
    private int age;
    protected double weight;
    public String className;
    
    public Person() {
    }
    
    private Person(int age) {
        
    }
    
    public Person(String name, int age, double weight, String className) {
        super();
        this.name = name;
        this.age = age;
        this.weight = weight;
        this.className = className;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className = className;
    }

    public String getName() {
        return name;
    }

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

    private int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", weight=" + weight
                + ", className=" + className + "]";
    }

    

}