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基本反射技术

技术反射 基本
2023-09-14 09:00:41 时间

--摘自《android插件化开发指南》

No1：

String str = "abc";
Class c1 = str.getClass();
System.out.print(c1.toString());
-------------
class java.lang.String

No2：

try {
    Class c2 = Class.forName("java.lang.String");
    Class c3 = Class.forName("android.widget.Button");
    Class c5 = c3.getSuperclass();

    System.out.println(c2.toString());
    System.out.println(c3.toString());
    System.out.println(c5.toString());
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}
--------------
class java.lang.String
class android.widget.Button
class android.widget.TextView

No3：

Class c6 = String.class;
Class c7 = java.lang.String.class;
Class c8 = MainActivity.class;
Class c9 = int.class;
Class c10 = int[].class;

System.out.println(c6.toString());
System.out.println(c7.toString());
System.out.println(c8.toString());
System.out.println(c9.toString());
System.out.println(c10.toString());
----------------
class java.lang.String
class java.lang.String
class com.example.jinke.joor.MainActivity
int
class [I

No4：

Class c11 = Boolean.TYPE;
Class c12 = Byte.TYPE;
Class c13 = Character.TYPE;
Class c14 = Short.TYPE;
Class c15 = Integer.TYPE;
Class c16 = Long.TYPE;
Class c17 = Float.TYPE;
Class c18 = Double.TYPE;
Class c19 = Void.TYPE;

System.out.println(c11.toString());
System.out.println(c12.toString());
System.out.println(c13.toString());
System.out.println(c14.toString());
System.out.println(c15.toString());
System.out.println(c16.toString());
System.out.println(c17.toString());
System.out.println(c18.toString());
System.out.println(c19.toString());
----------------------
boolean
byte
char
short
int
long
float
double
void

No5：

Class的getDeclaredConstructors方法可以获取所有构造函数，包括public和private的

public class TestClassCtor {
    String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }
}
public static void main(String[] args) {
    TestClassCtor r = new TestClassCtor();
    Class temp = r.getClass();
    String className = temp.getName();

    Constructor[] constructors = temp.getDeclaredConstructors();
    for (int i = 0; i < constructors.length; i++) {
        //mod是访问权限
        int mod = constructors[i].getModifiers();
        System.out.print(Modifier.toString(mod) + " " + className + "(");
        //parameterTypes是一个构造函数的参数类型
        Class[] parameterTypes = constructors[i].getParameterTypes();
        for (int j = 0; j < parameterTypes.length; j++) {
            System.out.print(parameterTypes[j].getName());
            if (parameterTypes.length > j + 1) {
                System.out.print(",");
            }
        }
        System.out.println(")");
    }
}
------------------------
private com.example.reflectiontest.TestClassCtor(int,double)
public com.example.reflectiontest.TestClassCtor(int,java.lang.String)
public com.example.reflectiontest.TestClassCtor(int)
public com.example.reflectiontest.TestClassCtor()

No6：

Class的getConstructors方法只能获得所有的public构造函数

public class TestClassCtor {
    String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }
}
public static void main(String[] args) {
    TestClassCtor r = new TestClassCtor();
    Class temp = r.getClass();
    try {
        //获取无参构造函数
        Constructor c1 = temp.getDeclaredConstructor();
        System.out.println(c1.toString());

        //获取一个参数（int型）构造函数
        Class[] p2 = {int.class};
        Constructor c2 = temp.getDeclaredConstructor(p2);
        System.out.println(c2.toString());

        //获取两个参数（int型、String型）
        Class[] p3 = {int.class, String.class};
        Constructor c3 = temp.getDeclaredConstructor(p3);
        System.out.println(c3.toString());
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    }
}
---------------
public com.example.reflectiontest.TestClassCtor()
public com.example.reflectiontest.TestClassCtor(int)
public com.example.reflectiontest.TestClassCtor(int,java.lang.String)

No7：

调用构造函数

public class TestClassCtor {
    String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }

    @Override
    public String toString() {
        return "name = " + name;
    }
}
try {
      Class r = Class.forName("com.example.reflectiontest.TestClassCtor");
      //含参
      Class[] p3 = {int.class, String.class};
      Constructor ctor = r.getDeclaredConstructor(p3);
      Object obj = ctor.newInstance(1, "bjq");
      System.out.println(obj.toString());

      //无参1
      Constructor ctor2 = r.getDeclaredConstructor();
      Object obj2 = ctor2.newInstance();
      System.out.println(obj2.toString());
      //无参2
      Object obj4 = r.newInstance();
      System.out.println(obj4.toString());

  } catch (Exception e) {
      e.printStackTrace();
  }
--------------------
name = bjq
name = baobao
name = baobao

No8：

调用私有实例方法

public class TestClassCtor {
    String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }

    private String doSomething(String d) {
        System.out.println("TestClassCtor,doSomething");
        return "123" + d;
    }

    private String doSomething2(String d, String e) {
        System.out.println("TestClassCtor,doSomething");
        return "123+" + d + "+" + e;
    }
}
try {
      Class r = Class.forName("com.example.reflectiontest.TestClassCtor");
      Class[] p3 = {int.class, String.class};
      Constructor ctor = r.getDeclaredConstructor(p3);
      Object obj = ctor.newInstance(1, "bjq");

      //调用私有方法1
      Class[] p4 = {String.class};
      Method method = r.getDeclaredMethod("doSomething", p4);
      method.setAccessible(true);

      Object argList[] = {"jianqiang"};
      Object result = method.invoke(obj, argList);
      System.out.println(result.toString());

      //调用私有方法2
      Class[] p5 = {String.class, String.class};
      Method method2 = r.getDeclaredMethod("doSomething2", p5);
      method2.setAccessible(true);

      Object argList2[] = {"jianqiang", "baobao"};
      Object result2 = method2.invoke(obj, argList2);
      System.out.println(result2.toString());

  } catch (Exception e) {
      e.printStackTrace();
  }
---------------
TestClassCtor,doSomething
123jianqiang
TestClassCtor,doSomething
123+jianqiang+baobao

我尝试了一下，如果doSomething是静态方法，上述代码照样适合

No9：

调用静态私有方法

public class TestClassCtor {
    String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }

    private static void work() {
        System.out.println("TestClassCtor,work");
    }
}
  try {
      Class r = Class.forName("com.example.reflectiontest.TestClassCtor");
      Method method = r.getDeclaredMethod("work");
      method.setAccessible(true);
      method.invoke(null);
  } catch (Exception e) {
      e.printStackTrace();
  }
-----------
TestClassCtor,work

这里没有创建实例，所以只能调静态方法

No10：

修改私有实例字段

public class TestClassCtor {
    private String name;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }

    public String getName() {
        return name;
    }
}
try {
    Class r = Class.forName("com.example.reflectiontest.TestClassCtor");
    Class[] p3 = {int.class, String.class};
    Constructor ctor = r.getDeclaredConstructor(p3);
    Object obj = ctor.newInstance(1, "bjq");

    Field field = r.getDeclaredField("name");
    field.setAccessible(true);
    Object fieldObject = field.get(obj);
    System.out.println(fieldObject.toString());

    field.set(obj, "jianqiang1982");
    fieldObject = field.get(obj);
    System.out.println(fieldObject.toString());
} catch (Exception e) {
    e.printStackTrace();
}
----------------------
bjq
jianqiang1982

我尝试了一下，如果name是静态私有变量，上述代码照样合适

No11：

修改私有静态字段

public class TestClassCtor {
    private String name;
    private static String address;

    public TestClassCtor() {
        name = "baobao";
    }

    public TestClassCtor(int a) {

    }

    public TestClassCtor(int a, String b) {
        name = b;
    }

    private TestClassCtor(int a, double c) {

    }

    public String getName() {
        return name;
    }

    public static void printAddress() {
        System.out.println(address);
    }
}
try {
    Class r = Class.forName("com.example.reflectiontest.TestClassCtor");
    Field field = r.getDeclaredField("address");
    field.setAccessible(true);

    Object fieldObject = field.get(null);
    field.set(fieldObject, "ABCD");

    System.out.println(field.get(fieldObject).toString());
    TestClassCtor.printAddress();
} catch (Exception e) {
    e.printStackTrace();
}
---------------------
ABCD
ABCD

No12：

对反省的反射

public abstract class Singleton {
    private T mInstance;

    protected abstract T create();

    public final T get() {
        synchronized (this) {
            if (mInstance == null) {
                mInstance = create();
            }
            return mInstance;
        }
    }
}
try {
    Class<?> singleton = Class.forName("com.example.reflectiontest.Singleton");
    Field mInstanceField = singleton.getDeclaredField("mInstance");
    mInstanceField.setAccessible(true);
} catch (Exception e) {
    e.printStackTrace();
}

以上

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