Java 反射：getMethods() 和 getDeclaredMethods() 之间的区别

Question

有人可以详细说明一下，并解释这两种方法之间的区别，以及何时/为什么要使用其中一种方法而不是其他方法

Answer 1

getDeclaredMethods includes all methods declared by the class itself , whereas getMethods returns only public methods, but also those inherited from a base class (here from java.lang.Object ).

Read more about it in the Javadocs for getDeclaredMethod and getMethods .

Answer 2

Short Version

Method	Public	Non-public	Inherited
getMethods()	✔️	❌	✔️
getDeclaredMethods()	✔️	✔️	❌

Long version

Methods	getMethods()	getDeclaredMethods
public	✔️	✔️
protected	❌	✔️
private	❌	✔️
static public	✔️	✔️
static protected	❌	✔️
static private	❌	✔️
default public	✔️	✔️
default protected	❌	✔️
default private	❌	✔️
inherited public	✔️	❌
inherited protected	❌	❌
inherited private	❌	❌
inherited static private	✔️	❌
inherited static protected	❌	❌
inherited static private	❌	❌
default inherited public	✔️	❌
default inherited protected	❌	❌
default inherited private	❌	❌

If your goal, like mine, was to get public methods of a class:

Method	Public	Non-public	Inherited
getMethods()	✔️	❌	✔️
getDeclaredMethods()	✔️	✔️	❌
getPublicMethods()	✔️	❌	❌

and nothing else:

Methods	getPublicMethods()
public	✔️
protected	❌
private	❌
static public	❌
static protected	❌
static private	❌
default public	❌
default protected	❌
default private	❌
inherited public	❌
inherited protected	❌
inherited private	❌
inherited static private	❌
inherited static protected	❌
inherited static private	❌
default inherited public	❌
default inherited protected	❌
default inherited private	❌

You have to do it yourself:

Iterable<Method> getPublicMethods(Object o) {
   List<Method> publicMethods = new ArrayList<>();

   // getDeclaredMethods only includes methods in the class (good)
   // but also includes protected and private methods (bad)
   for (Method method : o.getClass().getDeclaredMethods()) {
      if (!Modifier.isPublic(method.getModifiers())) continue; //only **public** methods
      if (!Modifier.isStatic(method.getModifiers())) continue; //only public **methods**
      publicMethods.add(method);
   }
   return publicMethods;
}