java反射超詳細講解

public class demo1Main1 {
    public static void main(String[] args) throws Exception {
        //獲取Class對象的三種對象
        System.out.println("根據類名：\t" + User.class);
        System.out.println("根據對象：\t" + new User().getClass());
        System.out.println("根據全限定類名：\t" + Class.forName("demo1.User"));
        //常用的方法
        Class<User> userClass = User.class;
        System.out.println("獲取全限定類名：\t" + userClass.getName());
        System.out.println("獲取類名：\t" + userClass.getSimpleName());
        System.out.println("實例化：\t" + userClass.newInstance());

    }
}

根據類名：	class demo1.User
根據對象：	class demo1.User
根據全限定類名：	class demo1.User
獲取全限定類名：	demo1.User
獲取類名：	User
實例化：	User{name='init', age=0}

public String toString() {
    return (isInterface() ? "interface " : (isPrimitive() ? "" : "class "))
        + getName();
}

package com.cry;
public class Test {
    private  class inner{
    }
    public static void main(String[] args) throws ClassNotFoundException {
        //普通類
        System.out.println(Test.class.getSimpleName()); //Test
        System.out.println(Test.class.getName()); //com.cry.Test
        System.out.println(Test.class.getCanonicalName()); //com.cry.Test
        //內部類
        System.out.println(inner.class.getSimpleName()); //inner
        System.out.println(inner.class.getName()); //com.cry.Test$inner
        System.out.println(inner.class.getCanonicalName()); //com.cry.Test.inner
        //數組
        System.out.println(args.getClass().getSimpleName()); //String[]
        System.out.println(args.getClass().getName()); //[Ljava.lang.String;
        System.out.println(args.getClass().getCanonicalName()); //java.lang.String[]
        //我們不能用getCanonicalName去加載類對象，必須用getName
        //Class.forName(inner.class.getCanonicalName()); 報錯
        Class.forName(inner.class.getName());
    }
}

public class ConstructionTest implements Serializable {
    public static void main(String[] args) throws Exception {
        Class<?> clazz = null;

        //獲取Class對象的引用
        clazz = Class.forName("com.example.javabase.User");

        //第一種方法，實例化默認構造方法，User必須無參構造函數,否則將拋異常
        User user = (User) clazz.newInstance();
        user.setAge(20);
        user.setName("Jack");
        System.out.println(user);

        System.out.println("--------------------------------------------");

        //獲取帶String參數的public構造函數
        Constructor cs1 =clazz.getConstructor(String.class);
        //創建User
        User user1= (User) cs1.newInstance("hiway");
        user1.setAge(22);
        System.out.println("user1:"+user1.toString());

        System.out.println("--------------------------------------------");

        //取得指定帶int和String參數構造函數,該方法是私有構造private
        Constructor cs2=clazz.getDeclaredConstructor(int.class,String.class);
        //由於是private必須設置可訪問
        cs2.setAccessible(true);
        //創建user對象
        User user2= (User) cs2.newInstance(25,"hiway2");
        System.out.println("user2:"+user2.toString());

        System.out.println("--------------------------------------------");

        //獲取所有構造包含private
        Constructor<?> cons[] = clazz.getDeclaredConstructors();
        // 查看每個構造方法需要的參數
        for (int i = 0; i < cons.length; i++) {
            //獲取構造函數參數類型
            Class<?> clazzs[] = cons[i].getParameterTypes();
            System.out.println("構造函數["+i+"]:"+cons[i].toString() );
            System.out.print("參數類型["+i+"]:(");
            for (int j = 0; j < clazzs.length; j++) {
                if (j == clazzs.length - 1)
                    System.out.print(clazzs[j].getName());
                else
                    System.out.print(clazzs[j].getName() + ",");
            }
            System.out.println(")");
        }
    }
}


class User {
    private int age;
    private String name;
    public User() {
        super();
    }
    public User(String name) {
        super();
        this.name = name;
    }

    /**
     * 私有構造
     * @param age
     * @param name
     */
    private User(int age, String name) {
        super();
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "User{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

User{age=20, name='Jack'}
--------------------------------------------
user1:User{age=22, name='hiway'}
--------------------------------------------
user2:User{age=25, name='hiway2'}
--------------------------------------------
構造函數[0]:private com.example.javabase.User(int,java.lang.String)
參數類型[0]:(int,java.lang.String)
構造函數[1]:public com.example.javabase.User(java.lang.String)
參數類型[1]:(java.lang.String)
構造函數[2]:public com.example.javabase.User()
參數類型[2]:()

Constructor cs3 = clazz.getDeclaredConstructor(int.class,String.class);
System.out.println("-----getDeclaringClass-----");
Class uclazz=cs3.getDeclaringClass();
//Constructor對象表示的構造方法的類
System.out.println("構造方法的類:"+uclazz.getName());

System.out.println("-----getGenericParameterTypes-----");
//對象表示此 Constructor 對象所表示的方法的形參類型
Type[] tps=cs3.getGenericParameterTypes();
for (Type tp:tps) {
    System.out.println("參數名稱tp:"+tp);
}
System.out.println("-----getParameterTypes-----");
//獲取構造函數參數類型
Class<?> clazzs[] = cs3.getParameterTypes();
for (Class claz:clazzs) {
    System.out.println("參數名稱:"+claz.getName());
}
System.out.println("-----getName-----");
//以字符串形式返回此構造方法的名稱
System.out.println("getName:"+cs3.getName());

System.out.println("-----getoGenericString-----");
//返回描述此 Constructor 的字符串，其中包括類型參數。
System.out.println("getoGenericString():"+cs3.toGenericString());

-----getDeclaringClass-----
構造方法的類:com.example.javabase.User
-----getGenericParameterTypes-----
參數名稱tp:int
參數名稱tp:class java.lang.String
-----getParameterTypes-----
參數名稱:int
參數名稱:java.lang.String
-----getName-----
getName:com.example.javabase.User
-----getoGenericString-----
getoGenericString():private com.example.javabase.User(int,java.lang.String)

public class ReflectField {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class<?> clazz = Class.forName("reflect.Student");
        //獲取指定字段名稱的Field類,註意字段修飾符必須為public而且存在該字段,
        // 否則拋NoSuchFieldException
        Field field = clazz.getField("age");
        System.out.println("field:"+field);

        //獲取所有修飾符為public的字段,包含父類字段,註意修飾符為public才會獲取
        Field fields[] = clazz.getFields();
        for (Field f:fields) {
            System.out.println("f:"+f.getDeclaringClass());
        }

        System.out.println("================getDeclaredFields====================");
        //獲取當前類所字段(包含private字段),註意不包含父類的字段
        Field fields2[] = clazz.getDeclaredFields();
        for (Field f:fields2) {
            System.out.println("f2:"+f.getDeclaringClass());
        }
        //獲取指定字段名稱的Field類,可以是任意修飾符的自動,註意不包含父類的字段
        Field field2 = clazz.getDeclaredField("desc");
        System.out.println("field2:"+field2);
    }
}

class Person{
    public int age;
    public String name;
    //省略set和get方法
}

class Student extends Person{
    public String desc;
    private int score;
    //省略set和get方法
}
  輸出結果: 
field:public int reflect.Person.age
f:public java.lang.String reflect.Student.desc
f:public int reflect.Person.age
f:public java.lang.String reflect.Person.name

================getDeclaredFields====================
f2:public java.lang.String reflect.Student.desc
f2:private int reflect.Student.score
field2:public java.lang.String reflect.Student.desc

//獲取Class對象引用
Class<?> clazz = Class.forName("reflect.Student");

Student st= (Student) clazz.newInstance();
//獲取父類public字段並賦值
Field ageField = clazz.getField("age");
ageField.set(st,18);
Field nameField = clazz.getField("name");
nameField.set(st,"Lily");

//隻獲取當前類的字段,不獲取父類的字段
Field descField = clazz.getDeclaredField("desc");
descField.set(st,"I am student");
Field scoreField = clazz.getDeclaredField("score");
//設置可訪問，score是private的
scoreField.setAccessible(true);
scoreField.set(st,88);
System.out.println(st.toString());

//輸出結果：Student{age=18, name='Lily ,desc='I am student', score=88} 

//獲取字段值
System.out.println(scoreField.get(st));
// 88

Class clazz = Class.forName("reflect.Circle");
//創建對象
Circle circle = (Circle) clazz.newInstance();

//獲取指定參數的方法對象Method
Method method = clazz.getMethod("draw",int.class,String.class);

//通過Method對象的invoke(Object obj,Object... args)方法調用
method.invoke(circle,15,"圈圈");

//對私有無參方法的操作
Method method1 = clazz.getDeclaredMethod("drawCircle");
//修改私有方法的訪問標識
method1.setAccessible(true);
method1.invoke(circle);

//對有返回值得方法操作
Method method2 =clazz.getDeclaredMethod("getAllCount");
Integer count = (Integer) method2.invoke(circle);
System.out.println("count:"+count);

draw 圈圈,count=15
drawCircle
count:100

public interface Type {
    //1.8新增
    default String getTypeName() {
        return toString();
    }
}