廖雪峰Java4反射与泛型-1反射-2访问字段Field和3调用方法Method

2.字段Field

2.1.通过Class实例获取字段field信息：

• getField(name): 获取某个public的field，包括父类
• getDeclaredField(name): 获取当前类的某个field，不包括父类
• getFields(): 获取所有public的field，包括父类
• getDeclaredFields(): 获取当前类的所有field，不包括父类

Hello.java

package com.reflection;

import java.util.ArrayList;

public interface Hello {
    ArrayList[] listname = new ArrayList[5];
    public void hello();
}

Student.java

package com.reflection;

public class Student implements Hello{
    private String name;
    public int age ;
    public Student(){
        this("unNamed");
    }
    public Student(String name){
        this.name=name;
    }
    public void hello(){
        System.out.println(name+" is Student");
    }
}

Main.java

package com.reflection;

import java.lang.reflect.Field;

public class Main {
    public static void main(String[] args) throws NoSuchFieldException{
        Class cls = Student.class;
        System.out.println("获取age："+cls.getField("age"));
        System.out.println();
        System.out.println("获取父类的listname："+cls.getField("listname"));
        System.out.println();
        System.out.println("获取age："+cls.getDeclaredField("age"));
        System.out.println();
        try{
            System.out.println("获取父类的listname："+cls.getDeclaredField("listname"));
        }catch (Exception e){
            System.out.println("获取父类的listname："+e);
        }
        System.out.println();
        System.out.println("获取全部的field，包含父类：");
        for(Field field:cls.getFields()){
            System.out.println(field);
        }
        System.out.println();
        System.out.println("获取全部的field，不包括父类：");
        for(Field field:cls.getDeclaredFields()){
            System.out.println(field);
        }
    }
}

2.2.Field对象包含一个field的所有信息：

• getName()
• getType()
• getModifiers()

JAVA 反射机制中，Field的getModifiers()方法返回int类型值表示该字段的修饰符。
其中，该修饰符是java.lang.reflect.Modifier的静态属性。
对应表如下：
PUBLIC: 1    PRIVATE: 2    PROTECTED: 4    STATIC: 8
FINAL: 16    SYNCHRONIZED: 32    VOLATILE: 64
TRANSIENT: 128    NATIVE: 256    INTERFACE: 512
ABSTRACT: 1024    STRICT: 2048

Main.java

package com.reflection;

import java.lang.reflect.Field;

public class Main {
    public static void main(String[] args) throws NoSuchFieldException{
        Class cls = Student.class;
        Field field1 = cls.getField("age");
        System.out.println(field1.getName());
        System.out.println(field1.getType());
        System.out.println(field1.getModifiers());
    }
}

2.3.获取和设置field的值：

• get(Object obj):
• set(Object,Object)

//疯狂Java840页
import java.lang.reflect.Field;

class Person {
    private String name;
    private int age;
    public String toString(){
        return "Person[name:" + name + ", age:" +age +"]";
    }
}
public class FieldTest{
    public static void main(String[] args) throws Exception{
        Class cls = Person.class;
        Person p = (Person) cls.newInstance();

        Field nameField = cls.getDeclaredField("name");
        nameField.setAccessible(true);
        nameField.set(p,"小明");

        Field ageField = cls.getDeclaredField("age");
        ageField.setAccessible(true);
        ageField.set(p,12);

        System.out.println(p.toString());
        System.out.println(ageField.get(p));
        System.out.println(nameField.get(p));
    }
}

2.4.通过反射访问Field需要通过SecurityManager设置的规则。

通过设置setAccessible(true)来访问非public字段。

3.调用方法Method

3.1通过class实例获取方法Method信息：

• getMethod(name,Class...)：获取某个public的method（包括父类）
• getDeclaredMethod(name,Class...)：获取当前类的某个method（不包括父类）
• getMethods()：获取所有public的method（包括父类）
• getDeclaredMethods()：获取当前类的所有method（不包括父类）
  
  Animal.java

package com.reflection;

public class Animal {
    public void run(){
        System.out.println("动物再跑");
    }
    private void eat(String s,String i){
        System.out.println("动物每天能吃"+i+"Kg"+s);
    }
}

Dog.java

package com.reflection;

public class Dog extends Animal {
    public void bar(){
        System.out.println("狗在叫");
    }
    private void func(){
        System.out.println("狗能看家");
    }
}

Go.java

package com.reflection;

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

public class Go {
    public static void main(String[] args) throws ClassNotFoundException,NoSuchMethodException,IllegalAccessException,InstantiationException,InvocationTargetException {
        Class cls = Class.forName("com.reflection.Dog");
        Dog dog = (Dog)cls.newInstance();

        System.out.println("getMethod获取某个public的method，包括父类");
        Method pubMethod1 = cls.getMethod("run");
        System.out.print(pubMethod1.getName()+":");
        pubMethod1.invoke(dog);
        Method pubMethod2 = cls.getMethod("bar");
        System.out.print(pubMethod2.getName()+":");
        pubMethod2.invoke(dog);
        System.out.println();

        System.out.println("getDeclaredMethod：获取当前类的某个method，不包括父类");
        Method subMethod1 = cls.getDeclaredMethod("func");
        System.out.println(subMethod1.getName());
        Method subMethod2 = cls.getDeclaredMethod("bar");
        System.out.println(subMethod2.getName());
        System.out.println();

        System.out.println("getMethods():获取所有public的method(包括父类)");
        for(Method m:cls.getMethods()){
            System.out.println(m.getName());
        }
        System.out.println();

        System.out.println("getDeclaredMethods():获取当前类的所有method(不包括父类)");
        for(Method m:cls.getDeclaredMethods()){
            System.out.println(m.getName());
        }
    }
}

## 3.2Method对象包含一个method的所有信息
* getName()
* getReturnType()
* getParameterTypes()
* getModifiers()
```#java
public class Go {
public static void main(String[] args) throws ClassNotFoundException,NoSuchMethodException,IllegalAccessException,InstantiationException,InvocationTargetException {
Class cls = Class.forName("com.reflection.Dog");
Dog dog = (Dog)cls.newInstance();
Method pubMethod1 = cls.getMethod("bar");
System.out.println(pubMethod1.getName());
System.out.println(pubMethod1.getReturnType());
System.out.println(pubMethod1.getParameterTypes());
System.out.println(pubMethod1.getModifiers());

}

}

<img src="https://img2018.cnblogs.com/blog/1418970/201902/1418970-20190219195137187-650653198.png" width="500" />

##    3.3调用Method：
*    Object invoke(Object obj,Object...args)
通过设置setAccessible(true)来访问非public方法
反射调用Method也遵守多态的规则
<font color=#9400D3>参见3.1中代码</font>
参考博客：
[https://blog.csdn.net/z69183787/article/details/23852517](https://blog.csdn.net/z69183787/article/details/23852517)
[https://blog.csdn.net/GhostFromHeaven/article/details/6498350](https://blog.csdn.net/GhostFromHeaven/article/details/6498350)