反射

反射获取构造方法对象并且创建对象

通过反射获取构造方法并且创建对象

* 1.通过反射获取字节码文件对象

* 2.通过字节码文件对象获取构造方法对象 Constructor

* Constructor<?>[] getConstructors() // 获取公有修饰的构造方法对象

* Constructor<?>[] getDeclaredConstructors() // 获取所有的构造方法对象

* Constructor<T> getConstructor(Class<?>... parameterTypes)

* Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)

public class ReflectDemo01 {

public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException {

Class<?> c = Class.forName("com.sxt.reflectdemo2.Student");

Constructor<?>[] constructors = c.getConstructors();

for (Constructor<?> constructor : constructors) {

System.out.println(constructor);

}

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

Constructor<?>[] declaredConstructors = c.getDeclaredConstructors();

for (Constructor<?> constructor : declaredConstructors) {

System.out.println(constructor);

}

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

// 获取所有的构造方法在开发中有意义? 没有什么实际意义，所以我们来获取单个构造方法

// 获取无参构造方法

// c.getConstructor(Class<?>... parameterTypes Class class)

Constructor<?> constructor = c.getConstructor();

System.out.println(constructor);

Constructor<?> constructor2 = c.getConstructor(String.class,int.class);

System.out.println(constructor2);

// 获取私有构造方法

// java.lang.NoSuchMethodException

// Constructor<?> constructor3 = c.getConstructor(String.class);

// System.out.println(constructor3);

Constructor<?> constructor3 = c.getDeclaredConstructor(String.class);

System.out.println(constructor3);

}

* 通过反射获取构造方法对象并且创建对象

* 反射之前的做法:

* Student s = new Student();

* 反射之后:

* 1.获取字节码文件对象

* 2.通过字节码文件对象获取构造方法对象

* 3.通过构造方法对象创建对象

* T newInstance(Object... initargs)

public class ReflectDemo02 {

public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException,

InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException,

FileNotFoundException, IOException {

Properties prop = new Properties();

prop.load(new FileReader("prop.txt"));

String value = prop.getProperty("ClassName");

Class<?> c = Class.forName(value);

Constructor<?> con = c.getConstructor();

Object obj = con.newInstance();

System.out.println(obj);

Student student = (Student) obj;

System.out.println(student.getName());

// 我想要调用带全参数的怎么办

Constructor<?> constructor = c.getConstructor(String.class, int.class);

Object obj2 = constructor.newInstance("隔壁老王", 50);

System.out.println(obj2);

// 我想获取私有构造方法并且造对象

// java.lang.NoSuchMethodException:

// Constructor<?> constructor2 = c.getConstructor(String.class);

Constructor<?> constructor2 = c.getDeclaredConstructor(String.class);

// java.lang.IllegalAccessException

// 暴力访问

constructor2.setAccessible(true);

Object obj3 = constructor2.newInstance("隔壁老李");

System.out.println(obj3);

}

反射获取成员变量对象并且赋值

通过反射获取成员变量对象

* Field

* Field[] getFields() 获取公有修饰的成员变量对象

* Field[] getDeclaredFields() 获取所有成员变量对象

* Field getField(String name) 获取指定的公共成员变量对象

* Field getDeclaredField(String name) 获取指定任意成员变量对象

* Object get(Object obj) 返回指定对象上此 Field 表示的字段的值。

public class ReflectDemo01 {

public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException {

Class<?> c = Class.forName("com.sxt.reflectdemo3.Student");

Field[] fields = c.getFields();

for (Field field : fields) {

System.out.println(field);

}

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

Field[] declaredFields = c.getDeclaredFields();

for (Field field : declaredFields) {

System.out.println(field);

}

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

// declaredFields

Field field = c.getField("address");

System.out.println(field);

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

Field field2 = c.getDeclaredField("name");

System.out.println(field2);

}

public class ReflectDemo02 {

public static void main(String[] args) throws Exception {

Class<?> c = Class.forName("com.sxt.reflectdemo3.Student");

// 给sex属性赋值，值为女

Field sexFiled = c.getDeclaredField("sex");

System.out.println(sexFiled);

// 反射之前 Student s = new Student(); s.sex = "女";

// 反射之后

Constructor<?> con = c.getDeclaredConstructor();

Object obj = con.newInstance();

// Object get(Object obj) 返回指定对象上此 Field 表示的字段的值。

sexFiled.set(obj, "女");

System.out.println(obj);

Field nameField = c.getDeclaredField("name");

nameField.setAccessible(true);

nameField.set(obj, "隔壁老张");

System.out.println(obj);

System.out.println(nameField.get(obj));

}

反射获取成员方法对象并且调用

通过反射获取成员方法对象并且调用

* c.getMethods() 获取所有公有方法包括父类继承过来的成员

* c.getDeclaredMethods() 获取本类中所有方法，包括私有

* Method getMethod(String name, Class<?>... parameterTypes)

* Method getDeclaredMethod(String name, Class<?>... parameterTypes)

* 第一个参数是方法名称, 第二个参数是参数类型列表

* Object invoke(Object obj, Object... args)

* 使用反射书写一个能够给任意对象设置任意的值的方法

public class ReflectDemo01 {

public static void main(String[] args) throws Exception {

Class<?> c = Class.forName("com.sxt.reflectdemo4.Student");

Constructor<?> con = c.getDeclaredConstructor();

Object obj = con.newInstance();

Method[] methods = c.getMethods();

for (Method method : methods) {

System.out.println(method);

}