java基础类-6-反射

常用类

java.lang.Class;                
java.lang.reflect.Constructor; 
java.lang.reflect.Field;        
java.lang.reflect.Method;
java.lang.reflect.Modifier;

获取类类型

Class c1 = Class.forName("Employee");   

Class c2 = Employee.class;  

Employeee = new Employee();  
Class c3 = e.getClass();

创建对象

Class c =Class.forName("Employee");  
Objecto = c.newInstance(); // 调用了Employee的无参构造方法

获取属性

Class c = Class.forName("java.lang.Integer");
Field[] fs = c.getDeclaredFields();
StringBuffer sb = new StringBuffer();
sb.append(Modifier.toString(c.getModifiers()) + " class " + c.getSimpleName() +"{\n");
for(Field field : fs) {
    sb.append("\t");
    sb.append(Modifier.toString(field.getModifiers())+" ");
    sb.append(field.getType().getSimpleName() + " ");
    sb.append(field.getName()+";\n");
}
sb.append("}");
System.out.println(sb);

获取特定属性

User u = new User();
u.age = 12;
System.out.println(u.age);

Class c = Class.forName("User");
Field idF = c.getDeclaredField("id");
Object o = c.newInstance();
idF.setAccessible(true); // 使用反射机制可以打破封装性，导致了java对象的属性不安全
idF.set(o, "110");
System.out.println(idF.get(o));

方法和构造方法

reflection-001.jpg

Class aClass = ... // obtain class object
Constructor[] constructors = aClass.getConstructors();
Constructor constructor = aClass.getConstructor(new Class[]{String.class}); // 参数不匹配，NoSuchMethodException
Class[] parameterTypes = constructor.getParameterTypes();

Constructor constructor = MyObject.class.getConstructor(String.class);
MyObject myObject = (MyObject) constructor.newInstance("constructor-arg1");