[Java] Reflection mechanism in java

Reflection mechanism in java

effect:

• JAVA reflection mechanism is in the running state, for any class, all the attributes and methods of this class can be known;
• For any object, any method and attribute can be called;
• The function of dynamically obtaining information and dynamically calling object methods is called the reflection mechanism of java language

Specific operation:

Examples:

package test;
 
public class Student {
    
    
	public Student(){
    
    
		
	}
	public Student(int num,String name){
    
    
		
	}
	private int num;
	
	public String name;
	
	protected String address;
}

Use reflection to get the class:

• To get the object of the class, use the object.getclass();

    Student st=new Student();
  
        st.getclass();
  

• Class name.class;

   Student.class;
  

• Class.forName("package name, class name");

  Class.forName("test、Student");
  

Use reflection to obtain constructors, attributes and methods in a class:

• Get the constructor in the class

    //测试类中的代码
        Class c=Student.class;
		//getConstructors只能获得公共构造器//getDeclaredConstructors获得所有构造器
        //constructor是获取构造器时所用
		Constructor[] cs= c.getConstructors;
		for (Constructor constructor : cs) {
    
    
		Student st=(Student)constructor.newInstance();
		System.out.println(st);
}
 

• Get the attributes in the class

  public class Test{
        
        
      
         public static void main(String[] args) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        
        
          //获得反射，获取属性的关键代码
   
          Class c=Student.class;
  		Field[] fs=	c.getDeclaredFields();
  		for (Field field : fs) {
        
        
  			System.out.println(field);
  		}
         //输出的结果为
         /*   private int com.qm.test.Student.num
          *   public java.lang.String com.qm.test.Student.name
          *   protected java.lang.String com.qm.test.Student.address
          */
  }
  }
  

• Get methods in the class

  public class Test{
        
        
      
         public static void main(String[] args) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        
        
       //获取方法的关键代码
   
          Class c=Student.class;
  		Method[] ms=c.getMethods();
  		for (Method method : ms) {
        
        
  			System.out.println(method);
  		}
   
      //此段代码将会输出Student类中继承了Object类的一些方法
   
  }
  }
  

  
  
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