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java反射例题【转载】

例题一 :简单例题

package pkg;
import java.lang.reflect.*;

public class Test {
 public static void main(String args[]) {
  try {
   Class c = Class.forName("java.lang.String");
   Method[] m = c.getDeclaredMethods();
   for (int i = 0; i < m.length; i++)
    System.out.println(m[i].toString());
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}

例题二:找出类的方法
package pkg;

import java.lang.reflect.*;

public class Test {
 private int methodDemo(Object p, int x) throws NullPointerException {
  if (p == null)
   throw new NullPointerException();
  return x;
 }

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Method[] methlist = cls.getDeclaredMethods();
   for (int i = 0; i < methlist.length; i++) {
    Method m = methlist[i];
    System.out.println("name = " + m.getName());
    System.out.println("decl class = " + m.getDeclaringClass());
    Class[] pvec = m.getParameterTypes();
    for (int j = 0; j < pvec.length; j++) {
     System.out.println("param #" + j + " " + pvec[j]);
    }
    Class[] evec = m.getExceptionTypes();
    for (int j = 0; j < evec.length; j++) {
     System.out.println("exc #" + j + " " + evec[j]);
    }
    System.out.println("return type = " + m.getReturnType());
    System.out.println("-----");
   }
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}
例题三:获取构造器信息

package pkg;

import java.lang.reflect.*;

public class Test {
 public Test() {
 }

 protected Test(int i, double d) {
 }

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Constructor[] ctorlist = cls.getDeclaredConstructors();
   for (int i = 0; i < ctorlist.length; i++) {
    Constructor ct = ctorlist[i];
    System.out.println("name = " + ct.getName());
    System.out.println("decl class = " + ct.getDeclaringClass());
    Class[] pvec = ct.getParameterTypes();
    for (int j = 0; j < pvec.length; j++) {
     System.out.println("param #" + j + " " + pvec[j]);
    }
    Class[] evec = ct.getExceptionTypes();
    for (int j = 0; j < evec.length; j++) {
     System.out.println("exc #" + j + " " + evec[j]);
    }
    System.out.println("-----------------------------------------------------");
   }
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}

例题四:获取类的字段(域)

package pkg;

import java.lang.reflect.*;

public class Test {
 private double d;
 public static final int i = 37;
 String s = "testing";

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Field[] fieldlist = cls.getDeclaredFields();//cls.getFields()
   for (int i = 0; i < fieldlist.length; i++) {
    Field fld = fieldlist[i];
    System.out.println("name = " + fld.getName());
    System.out.println("decl class = " + fld.getDeclaringClass());
    System.out.println("type = " + fld.getType());
    int mod = fld.getModifiers();
    System.out.println("modifiers = " + Modifier.toString(mod));
    System.out.println("-----------------------------------------------------");
   }
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}
例题五:根据方法的名称来执行方法
package pkg;

import java.lang.reflect.*;

public class Test {
 public int add(int a, int b) {
  return a + b;
 }

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Class[] partypes = new Class[2];
   partypes[0] = Integer.TYPE;
   partypes[1] = Integer.TYPE;
   Method meth = cls.getMethod("add", partypes);
   //Test methobj = new Test();
   Object methobj = cls.newInstance();
   Object[] arglist = new Object[2];
   arglist[0] = new Integer(37);
   arglist[1] = new Integer(47);
   Object retobj = meth.invoke(methobj, arglist);
   Integer retval = (Integer) retobj;
   System.out.println(retval.intValue());
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}

例题六:创建新的对象

package pkg;

import java.lang.reflect.*;

public class Test {
 public Test() {
 }

 public Test(int a, int b) {
  System.out.println("a = " + a + " b = " + b);
 }

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Class[] partypes = new Class[2];
   partypes[0] = Integer.TYPE;
   partypes[1] = Integer.TYPE;
   Constructor ct = cls.getConstructor(partypes);
   Object[] arglist = new Object[2];
   arglist[0] = new Integer(37);
   arglist[1] = new Integer(47);
   Object retobj = ct.newInstance(arglist);

  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}
例题七:.改变字段(域)的值
package pkg;

import java.lang.reflect.*;

public class Test {
 public double d;

 public static void main(String args[]) {
  try {
   Class cls = Class.forName("pkg.Test");
   Field fld = cls.getField("d");
   Test test = new Test();
   System.out.println("d = " + test.d);
   fld.setDouble(test, 12.34);
   System.out.println("d = " + test.d);
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}
例题八:数组

package pkg;

import java.lang.reflect.*;

public class Test {
 public static void main(String args[]) {
  try {
   Class cls = Class.forName("java.lang.String");
   Object arr = Array.newInstance(cls, 10);
   Array.set(arr, 5, "this is a test");
   String s = (String) Array.get(arr, 5);
   System.out.println(s);
  } catch (Throwable e) {
   System.err.println(e);
  }
 }
}

例题九:5 x 10 x 15 的整型数组

package pkg;

import java.lang.reflect.*;

public class Test {
 public static void main(String args[]) {
  int[] dims = new int[] { 5, 10, 15 };
  Object arr = Array.newInstance(Integer.TYPE, dims);
  Object arrobj = Array.get(arr, 3);
  Class cls = arrobj.getClass().getComponentType();
  System.out.println(cls);
  arrobj = Array.get(arrobj, 5);
  Array.setInt(arrobj, 10, 37);
  int arrcast[][][] = (int[][][]) arr;
  System.out.println(arrcast[3][5][10]);
 }
}




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posted on 2009-04-18 15:04 liudecai_zan@126.com 阅读(252) 评论(0)  编辑  收藏 所属分类: 程序人生


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