Java: Analysis of Reflection Mechanism

I thought about a question before, whether it is possible to call a method in a class through a string. Baidu has been using the reflection mechanism for a long time to achieve the functions I want.

Let's take a look at the solution to my problem:

// 通过包名.类名得到Class对象
String info = "java.util.HashMap";
Class<?> demo = Class.forName(info);
// 通过demo对象获取实例
HashMap<String, String> hashMap = (HashMap<String, String>) demo.newInstance();
		
// 调用自带的put函数
hashMap.put("a", "1");
System.out.println("=========put函数调用后=========");
System.out.println(hashMap);
		
// 通过反射机制，得到remove方法
Method method = demo.getDeclaredMethod("remove", Class.forName("java.lang.Object"));
// 调用remove方法
method.invoke(hashMap, "a");
System.out.println("=========通过反射remove函数调用后=========");
System.out.println(hashMap);

Program running results:

=========put函数调用后=========
{a=1}
=========通过反射remove函数调用后=========
{}

We understand what Java's reflection mechanism can do.

Get method name

String info = "java.util.HashMap";
Class<?> demo = Class.forName(info);
Method[] methods = demo.getDeclaredMethods();
for (Method method : methods) {
	System.out.println(method);
}

Program running results:

public java.lang.Object java.util.HashMap.remove(java.lang.Object)
public boolean java.util.HashMap.remove(java.lang.Object,java.lang.Object)
public java.lang.Object java.util.HashMap.get(java.lang.Object)
......

Get attributes

String info = "java.util.HashMap";
Class<?> demo = Class.forName(info);
Field[] fields = demo.getDeclaredFields();
for (Field field : fields) {
	System.out.println(field);
}

Program running results:

private static final long java.util.HashMap.serialVersionUID
static final int java.util.HashMap.DEFAULT_INITIAL_CAPACITY
static final int java.util.HashMap.MAXIMUM_CAPACITY
......

Get the parent class

String info = "java.util.HashMap";
Class<?> demo = Class.forName(info);
System.out.println(demo.getSuperclass());

Program running results:

class java.util.AbstractMap

Call class constructor

String info = "java.util.HashMap";
Class<?> demo = Class.forName(info);
// 通过demo对象获取实例
HashMap<String, String> hashMap = (HashMap<String, String>) demo.newInstance();

newInstance() is to call the constructor, and the no-argument constructor is called. If you need to carry parameters, just add it directly.

Now think about it, many J2EE frameworks that rely on xml may use the reflection mechanism.

Java: Analysis of Reflection Mechanism

Guess you like