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Using the java.lang.reflect.Modifier Class

R.Zeus — Wed, 13 Sep 2006 08:10:00 GMT

Using the java.lang.reflect.Modifier Class

You know that you can extract constructors, methods, and variables from a Java class file. Generally, when you use


	Field fields[] = c.getDeclaredFields( );

where c is initialized using


	Class c = Class.forName(className);

and print the fields array, you get all the elements declared in the class.

However, suppose you want to restrict the output to all fields other than those declared as private. In this case, you would use the following code, where the Modifier class is a part of the java.lang.reflect package:


if(!Modifier.isPrivate(fields[i].getModifiers( )){
	System.out.println(fields[i]+"\n");
}

Using Modifier.isPrivate() ensures that the private variables are not printed.

The same can be used for methods as well.

author: MS Sridhar

R.Zeus 2006-09-13 16:10 发表评论

receive type name from type value

R.Zeus — Wed, 13 Sep 2006 03:01:00 GMT

in hibernate , ASTPrinter receive the HqlTokenTypes name by an int value.how did it do?
first ,useing Class.getFields to get all the fields,the use filed.get(null) to get the field's value that equals the int type will be returned.
so ,field.get(null) can return the field's value.if the parameter nonequals null,what it will return?
in addition,when use field.get(null),it use Modifier.isStatic( field.getModifiers() ) to check weather the filed is static.why it do this?if the field isn't static ,it will be what?
in my next test,
only public field can recieved by Class.getFields,even the page-privilege can't.
and only the static field can be return it's value when use filed.get(null),else will be error.

R.Zeus 2006-09-13 11:01 发表评论

example:DynTest.java

R.Zeus — Tue, 23 Aug 2005 13:25:00 GMT

import java.lang.reflect.*;
import java.util.*;

public class DynTest {
     public double d; // a field

      public int add(int a, int b)
      {
      System.out.println("add() invoked");
         return a + b;
      }
      public String tName(String s, Hashtable ht)
      {
      System.out.println("tName() invoked");
         return s;
      }

      public static void main(String args[])
      {
      //代刚1. Method.invoke()
        {
         try {
                   Class c = Class.forName("DynTest");
            Class pTypes[] = new Class[2];
            pTypes[0] = Integer.TYPE;
            pTypes[1] = Integer.TYPE;
                      Method m = c.getMethod("add", pTypes);

                    DynTest obj = new DynTest();

                        Object arg[] = new Object[2];
            arg[0] = new Integer(37);
            arg[1] = new Integer(47);

                     Object r = m.invoke(obj, arg);
            Integer rVal = (Integer)r;
            System.out.println("return: "+rVal.intValue()); //84
         }
         catch (Throwable e) {
            System.err.println(e);
         }
        }

        //代刚2. Method.invoke()
        {
         try {
                       Class c = Class.forName("DynTest");
            Class pTypes[] = new Class[2];
            pTypes[0] = Class.forName("java.lang.String");
            pTypes[1] = Class.forName("java.util.Hashtable");
                      Method m = c.getMethod("tName", pTypes);

                      Object arg[] = new Object[2];
            arg[0] = new String("return: "+"Hello,World!");
            arg[1] = null;

          //ERROR: non-static variable this cannot be referenced from a static context
                      DynTest obj = new DynTest();
            Object r = m.invoke(obj, arg);
            String rVal = (String)r;
            System.out.println(rVal); //Hello,World!
         }
         catch (Throwable e) {
            System.err.println(e);
         }
        }

        //代刚3. Field.setDouble()
        {
         try {
            Class c = Class.forName("DynTest");
            Field f = c.getField("d");
            DynTest obj = new DynTest();
            System.out.println("before setting, d= " + obj.d); //0.0
            f.setDouble(obj, 12.34);
            System.out.println("after setting, d= " + obj.d); //12.34
         }
         catch (Throwable e) {
            System.err.println(e);
         }
        }

      } //main
}

R.Zeus 2005-08-23 21:25 发表评论

“Class” object的取得途径

R.Zeus — Tue, 23 Aug 2005 13:21:00 GMT

Java允许我们从多种管道为一个class生成对应的Class object。图2是一份整理。

Class object 诞生管道

示例

运用getClass()

注：每个class 都有此函数

String str = "abc";

Class c1 = str.getClass();

运用

Class.getSuperclass()²

Button b = new Button();

Class c1 = b.getClass();

Class c2 = c1.getSuperclass();

运用static method

Class.forName()

（最常被使用）

Class c1 = Class.forName ("java.lang.String");

Class c2 = Class.forName ("java.awt.Button");

Class c3 = Class.forName ("java.util.LinkedList$Entry");

Class c4 = Class.forName ("I");

Class c5 = Class.forName ("[I");

运用

.class 语法

Class c1 = String.class;

Class c2 = java.awt.Button.class;

Class c3 = Main.InnerClass.class;

Class c4 = int.class;

Class c5 = int[].class;

运用

primitive wrapper classes

的TYPE 语法

Class c1 = Boolean.TYPE;

Class c2 = Byte.TYPE;

Class c3 = Character.TYPE;

Class c4 = Short.TYPE;

Class c5 = Integer.TYPE;

Class c6 = Long.TYPE;

Class c7 = Float.TYPE;

Class c8 = Double.TYPE;

Class c9 = Void.TYPE;

R.Zeus 2005-08-23 21:21 发表评论