在面向对象的世界里，万物皆对象。类是对象，类是java.lang.Class类的实例对象。另外class类只有java虚拟机才能new出来。任何一个类都是Class。 类的实例对象。这实例对象有三种表达方式：
Class s1=Class.forName("com.lmr.invoke.Student"); Class s2=Student.class; Student s=new Student(); Class s3=s.getClass();Class.forName(类的全称);该方法不仅表示了类的类型，还代表了动态加载类。编译时刻加载类是静态加载、运行时刻加载类是动态加载类。
可以利用==运算符实现两个类对象的比较
if(e.getClass()==xx.class){ }newInstance()可以用来快速创建一个类的实例,前提是该类必须存在一个无参构造方法.
e.getClass.newInstance()eg1：
private static void initClass() throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException { // TODO Auto-generated method stub //三种实例方式 Class s1=Class.forName("com.lmr.invoke.Student"); Class s2=Student.class; Student s=new Student(1,"1",1); Class s3=s.getClass(); System.out.println(s1.getName()); System.out.println(s1.getSimpleName()); System.out.println(s2.getName()); System.out.println(s3.getName()); Student stu1=(Student) s1.newInstance();//通过类的类型创建该类的实例对象 ，前提是该类必须存在一个无参构造方法 Constructor con=s2.getConstructor(int.class,String.class,int.class);//取得指定参数类型的构造方法 Student stu2=(Student) con.newInstance(1,"name",12); System.out.println(stu1.toString()); System.out.println(stu2.toString()); }结果：
com.lmr.invoke.Student Student com.lmr.invoke.Student com.lmr.invoke.Student Student [id=0, name=null, age=0] Student [id=1, name=name, age=12]通过反射来获取类的结构。 Class类中的getFields()、getMethods()、getConstructors()方法将分别返回类提供的public域、方法和构造器数组，其中包括超类的公有成员。 eg2：
private static void initClassInfo() { // TODO Auto-generated method stub // Class c=Student.class; Class c=Math.class; System.out.println(c.getName()); System.out.println(c.getSimpleName()); // System.out.println(c.getComponentType()); // Field[] fields=c.getFields();//获取public类型的成员变量 Field[] fields=c.getDeclaredFields();//成员变量信息,获取全部 System.out.println("----------成员变量----------"); for(Field f:fields){ int mod=f.getModifiers(); String modtype=Modifier.toString(mod);//方法的属性 System.out.println(modtype+" "+f.getType().getSimpleName()+" "+f.getName()); } Constructor[] constructors=c.getDeclaredConstructors();//获取构造函数信息 System.out.println("----------构造函数----------"); for(Constructor con:constructors){ String name=con.getName();//方法名 Class[] paramterType=con.getParameterTypes();//方法中参数类型 int mod=con.getModifiers(); String modtype=Modifier.toString(mod);//方法的属性 System.out.print(modtype+" "+name+" ("); for(Class p:paramterType){ System.out.print(p.getSimpleName()+" "); } System.out.println(")"); } Method[] methods=c.getMethods();//获取函数方法信息 System.out.println("-----------方法-----------"); for(Method m:methods){ String name=m.getName();//方法名 Class returnType=m.getReturnType();//方法返回类型 Class[] paramterType=m.getParameterTypes();//方法中参数类型 int mod=m.getModifiers(); String modtype=Modifier.toString(mod);//方法的属性 System.out.print(modtype+" "+returnType.getSimpleName()+" "+name+" ("); for(Class p:paramterType){ System.out.print(p.getSimpleName()+" "); } System.out.println(")"); } }结果：
java.lang.Math Math ----------成员变量---------- public static final double E public static final double PI private static long negativeZeroFloatBits private static long negativeZeroDoubleBits static double twoToTheDoubleScaleUp static double twoToTheDoubleScaleDown static final boolean $assertionsDisabled ----------构造函数---------- private java.lang.Math () -----------方法----------- public static int abs (int ) public static double abs (double ) public static float abs (float ) public static long abs (long ) public static double sin (double ) public static double cos (double ) public static double tan (double ) public static double atan2 (double double ) public static double sqrt (double ) public static double log (double ) public static double log10 (double ) public static double pow (double double ) public static double exp (double ) public static long min (long long ) public static double min (double double ) public static float min (float float ) public static int min (int int ) public static double max (double double ) public static float max (float float ) public static long max (long long ) public static int max (int int ) public static long addExact (long long ) public static int addExact (int int ) public static int decrementExact (int ) public static long decrementExact (long ) public static long incrementExact (long ) public static int incrementExact (int ) public static long multiplyExact (long long ) public static int multiplyExact (int int ) public static int negateExact (int ) public static long negateExact (long ) public static int subtractExact (int int ) public static long subtractExact (long long ) public static double scalb (double int ) public static float scalb (float int ) public static double copySign (double double ) public static float copySign (float float ) public static int getExponent (float ) public static int getExponent (double ) public static double signum (double ) public static float signum (float ) public static double IEEEremainder (double double ) public static double acos (double ) public static double asin (double ) public static double atan (double ) public static double cbrt (double ) public static double ceil (double ) public static double cosh (double ) public static double expm1 (double ) public static double floor (double ) public static long floorDiv (long long ) public static int floorDiv (int int ) public static int floorMod (int int ) public static long floorMod (long long ) public static double hypot (double double ) public static double log1p (double ) public static float nextAfter (float double ) public static double nextAfter (double double ) public static double nextDown (double ) public static float nextDown (float ) public static double nextUp (double ) public static float nextUp (float ) public static double random () public static double rint (double ) public static int round (float ) public static long round (double ) public static double sinh (double ) public static double tanh (double ) public static double toDegrees (double ) public static int toIntExact (long ) public static double toRadians (double ) public static double ulp (double ) public static float ulp (float ) public final void wait () public final void wait (long int ) public final native void wait (long ) public boolean equals (Object ) public String toString () public native int hashCode () public final native Class getClass () public final native void notify () public final native void notifyAll ()获取一个方法：需要获取方法的名称和方法的参数才能决定一个方法。
Class[] paramtype={int.class, int.class}; Method m=calculateclass.getMethod("add", paramtype); Method m=calculateclass.getMethod("add", int.class, int.class);方法的反射操作：method.invoke(对象，参数列表);
eg1：
public static void InvokeOne(){ try { Class calculateclass=Class.forName("com.lmr.invoke.Calculate"); Class[] paramtype={int.class, int.class}; Method m=calculateclass.getMethod("add", paramtype); // Method m=calculateclass.getMethod("add", int.class, int.class); m.invoke(calculateclass.newInstance(), 1, 2);//method.invoke(对象，参数列表); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (NoSuchMethodException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SecurityException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IllegalAccessException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IllegalArgumentException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InstantiationException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public class Calculate { public void add(int a,int b){ System.out.println(a+b); } public void subtract(int a,int b){ System.out.println(a-b); } public void multiply(int a,int b){ System.out.println(a*b); } public void divide(int a,int b){ if(b!=0){ System.out.println(a/b); } } }结果：打印出1+2的结果，3
Java的反射机制的实现要借助于4个类：class，Constructor，Field，Method; class－类对象 Constructor－类的构造器对象 Field－类的属性对象 Method－类的方法对象
反射的操作都是在运行时进行的
private static void InvokeTwo() { // TODO Auto-generated method stub try { Class studentclass=Class.forName("com.lmr.invoke.Student"); Object stuobj=studentclass.newInstance(); Method setStuName=studentclass.getMethod("setName", String.class); setStuName.invoke(stuobj, "Jack"); // PropertyDescriptor pd=new PropertyDescriptor("name", studentclass);//通过属性名来获取对应的存储器，从而获取其get，set方法 // Method setStuName=pd.getWriteMethod(); Method toStuString=studentclass.getMethod("toString"); System.out.println(toStuString.invoke(stuobj)); Field name=studentclass.getDeclaredField("name"); name.setAccessible(true);//由于name是一个私有域，所有须解除封装 name.set(stuobj, "Jane"); System.out.println(toStuString.invoke(stuobj)); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InstantiationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IllegalAccessException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (NoSuchMethodException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SecurityException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IllegalArgumentException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (NoSuchFieldException e) { // TODO Auto-generated catch block e.printStackTrace(); } }结果：
Student [id=0, name=Jack, age=0] Student [id=0, name=Jane, age=0]