java中的reflect机制!!!
Java Reflection (JAVA反射)
Reflection 是 Java 程序开发语言的特征之一，它允许运行中的 Java 程序对自身进行检查，或者说“自审”，并能直接操作程序的内部属性。例如，使用它能获得 Java 类中各成员的名称并显示出来。
Java 的这一能力在实际应用中也许用得不是很多，但是在其它的程序设计语言中根本就不存在这一特性。例如，Pascal、C 或者 C++ 中就没有办法在程序中获得函数定义相关的信息。
JavaBean 是 reflection 的实际应用之一，它能让一些工具可视化的操作软件组件。这些工具通过 reflection 动态的载入并取得 Java 组件(类) 的属性。
1. 一个简单的例子
考虑下面这个简单的例子，让我们看看 reflection 是如何工作的。
import java.lang.reflect.*;public class DumpMethods { public static void main(String args[]) { try { Class c = Class.forName(args[0]); 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); } }}class A {}public class instance1 { public static void main(String args[]) { try { Class cls = Class.forName("A"); boolean b1 = cls.isInstance(new Integer(37)); System.out.println(b1); boolean b2 = cls.isInstance(new A()); System.out.println(b2); } catch (Throwable e) { System.err.println(e); } }}import java.lang.reflect.*;public class method1 { private int f1(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("method1"); 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); } }}import java.lang.reflect.*;public class constructor1 { public constructor1() { } protected constructor1(int i, double d) { } public static void main(String args[]) { try { Class cls = Class.forName("constructor1"); 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); } }}import java.lang.reflect.*;public class field1 { private double d; public static final int i = 37; String s = "testing"; public static void main(String args[]) { try { Class cls = Class.forName("field1"); Field fieldlist[] = cls.getDeclaredFields(); 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); } }}import java.lang.reflect.*;public class method2 { public int add(int a, int b) { return a + b; } public static void main(String args[]) { try { Class cls = Class.forName("method2"); Class partypes[] = new Class[2]; partypes[0] = Integer.TYPE; partypes[1] = Integer.TYPE; Method meth = cls.getMethod("add", partypes); method2 methobj = new method2(); 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); } }}import java.lang.reflect.*;public class constructor2 { public constructor2() { } public constructor2(int a, int b) { System.out.println("a = " + a + " b = " + b); } public static void main(String args[]) { try { Class cls = Class.forName("constructor2"); 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); } }}import java.lang.reflect.*;public class field2 { public double d; public static void main(String args[]) { try { Class cls = Class.forName("field2"); Field fld = cls.getField("d"); field2 f2obj = new field2(); System.out.println("d = " + f2obj.d); fld.setDouble(f2obj, 12.34); System.out.println("d = " + f2obj.d); } catch (Throwable e) { System.err.println(e); } }}import java.lang.reflect.*;public class array1 { 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); } }}import java.lang.reflect.*;public class array2 { 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]); }}