彻底了解类的构成

Java的RTTI(Run Time Type Identification)提供了很多手段,可以让程序员更好的了解类的构成,即类到底有哪些函数,有哪些成员,这对我们更好的理解类以及其他相关概念有很大的帮助.

 

这需要用类Class中有函数getMethods(),getDeclaredFields()来完成,在<Thinking in Java>中, Bruce Eckel写了个ShowMethods的工具类,”依葫芦画瓢”,我写了ShowFields类,这两个工具类就可以帮助我们来解剖任何一个类了,很有用吧!

 

No.1 ShowMethods.java

import java.lang.reflect.*;

public class ShowMethods {
  static final String usage =
    "usage: \n" +
    "ShowMethods qualified.class.name\n" +
    "To show all methods in class or: \n" +
    "ShowMethods qualified.class.name word\n" +
    "To search for methods involving 'word'";
  public static void main(String[] args) {
    if(args.length < 1) {
      System.out.println(usage);
      System.exit(0);
    }
    try {
      Class c = Class.forName(args[0]);
      Method[] m = c.getMethods();
      Constructor[] ctor = c.getConstructors();
      if(args.length == 1) {
        for (int i = 0; i < m.length; i++)
          System.out.println(m[i].toString());
        for (int i = 0; i < ctor.length; i++)
          System.out.println(ctor[i].toString());
      } 
      else {
        for (int i = 0; i < m.length; i++)
          if(m[i].toString()
             .indexOf(args[1])!= -1)
            System.out.println(m[i].toString());
        for (int i = 0; i < ctor.length; i++)
          if(ctor[i].toString()
             .indexOf(args[1])!= -1)
          System.out.println(ctor[i].toString());
      }
    } catch (ClassNotFoundException e) {
      System.out.println("No such class: " + e);
    }
  }
} ///:~

 

 

 

No.2 ShowFields.java

import java.lang.reflect.*;

public class ShowFields {
	
  static final String usage =
    "usage: \n" +
    "ShowFields qualified.class.name\n" +
    "To show all fields in class or: \n" +
    "ShowFields qualified.class.name word\n" +
    "To search for fields involving 'word'";
    
  public static void main(String[] args) {
    if(args.length < 1) {
      System.out.println(usage);
      System.exit(0);
    }
    try {
      Class c = Class.forName(args[0]);
      Field[] f = c.getDeclaredFields();
			
      if(args.length == 1) {
        for (int i = 0; i < f.length; i++)
          System.out.println(f[i].toString());
      } 
      else {
        for (int i = 0; i < f.length; i++)
          if(f[i].toString()
             .indexOf(args[1])!= -1)
            System.out.println(f[i].toString());
      }
    } catch (ClassNotFoundException e) {
      System.out.println("No such class: " + e);
    }
  }
} ///:~