一:定义
能够分析类能力的程序称为反射。
二:分析:
三:反射机制的功能:
1.在运行中分析类的能力;
2.在运行中查看对象;
3.实现通用的数组操作代码;
4.利用Method对象,这个对象很像C++中的函数指针。----From CoreJava
或者:
四:Class类
在JDK中,主要由以下类来实现Java反射机制,这些类都位于java.lang.reflect包中:
五:实例
public class RefConstructor {
public static void main(String args[]) throws Exception {
RefConstructor ref = new RefConstructor();
ref.getConstructor();
}
public void getConstructor() throws Exception {
Class c = null;
c = Class.forName("java.lang.Long");
Class cs[] = {java.lang.String.class};
System.out.println("\n-------------------------------\n");
Constructor cst1 = c.getConstructor(cs);
System.out.println("1、通过参数获取指定Class对象的构造方法:");
System.out.println(cst1.toString());
Constructor cst2 = c.getDeclaredConstructor(cs);
System.out.println("2、通过参数获取指定Class对象所表示的类或接口的构造方法:");
System.out.println(cst2.toString());
Constructor cst3 = c.getEnclosingConstructor();
System.out.println("3、获取本地或匿名类Constructor 对象,它表示基础类的立即封闭构造方法。");
if (cst3 != null) System.out.println(cst3.toString());
else System.out.println("-- 没有获取到任何构造方法!");
Constructor[] csts = c.getConstructors();
System.out.println("4、获取指定Class对象的所有构造方法:");
for (int i = 0; i < csts.length; i++) {
System.out.println(csts[i].toString());
}
System.out.println("\n-------------------------------\n");
Type[] types1 = c.getGenericInterfaces();
System.out.println("1、返回直接实现的接口:");
for (int i = 0; i < types1.length; i++) {
System.out.println(types1[i].toString());
}
Type type1 = c.getGenericSuperclass();
System.out.println("2、返回直接超类:");
System.out.println(type1.toString());
Class[] cis = c.getClasses();
System.out.println("3、返回超类和所有实现的接口:");
for (int i = 0; i < cis.length; i++) {
System.out.println(cis[i].toString());
}
Class cs1[] = c.getInterfaces();
System.out.println("4、实现的接口");
for (int i = 0; i < cs1.length; i++) {
System.out.println(cs1[i].toString());
}
System.out.println("\n-------------------------------\n");
java.lang.reflect.Field[] fs1 = c.getFields();
System.out.println("1、类或接口的所有可访问公共字段:");
for (int i = 0; i < fs1.length; i++) {
System.out.println(fs1[i].toString());
}
java.lang.reflect.Field f1 = c.getField("MIN_VALUE");
System.out.println("2、类或接口的指定已声明指定公共成员字段:");
System.out.println(f1.toString());
java.lang.reflect.Field[] fs2 = c.getDeclaredFields();
System.out.println("3、类或接口所声明的所有字段:");
for (int i = 0; i < fs2.length; i++) {
System.out.println(fs2[i].toString());
}
java.lang.reflect.Field f2 = c.getDeclaredField("serialVersionUID");
System.out.println("4、类或接口的指定已声明指定字段:");
System.out.println(f2.toString());
System.out.println("\n-------------------------------\n");
Method m1[] = c.getMethods();
System.out.println("1、返回类所有的公共成员方法:");
for (int i = 0; i < m1.length; i++) {
System.out.println(m1[i].toString());
}
Method m2 = c.getMethod("longValue", new Class[]{});
System.out.println("2、返回指定公共成员方法:");
System.out.println(m2.toString());
}
}
-------------------------------
1、通过参数获取指定Class对象的构造方法:
public java.lang.Long(java.lang.String) throws java.lang.NumberFormatException
2、通过参数获取指定Class对象所表示的类或接口的构造方法:
public java.lang.Long(java.lang.String) throws java.lang.NumberFormatException
3、获取本地或匿名类Constructor 对象,它表示基础类的立即封闭构造方法。
-- 没有获取到任何构造方法!
4、获取指定Class对象的所有构造方法:
public java.lang.Long(long)
public java.lang.Long(java.lang.String) throws java.lang.NumberFormatException
-------------------------------
1、返回直接实现的接口:
java.lang.Comparable<java.lang.Long>
2、返回直接超类:
class java.lang.Number
3、返回超类和所有实现的接口:
4、实现的接口
interface java.lang.Comparable
-------------------------------
1、类或接口的所有可访问公共字段:
public static final long java.lang.Long.MIN_VALUE
public static final long java.lang.Long.MAX_VALUE
public static final java.lang.Class java.lang.Long.TYPE
public static final int java.lang.Long.SIZE
2、类或接口的指定已声明指定公共成员字段:
public static final long java.lang.Long.MIN_VALUE
3、类或接口所声明的所有字段:
public static final long java.lang.Long.MIN_VALUE
public static final long java.lang.Long.MAX_VALUE
public static final java.lang.Class java.lang.Long.TYPE
private final long java.lang.Long.value
public static final int java.lang.Long.SIZE
private static final long java.lang.Long.serialVersionUID
4、类或接口的指定已声明指定字段:
private static final long java.lang.Long.serialVersionUID
-------------------------------
1、返回类所有的公共成员方法:
public static int java.lang.Long.numberOfLeadingZeros(long)
public static int java.lang.Long.numberOfTrailingZeros(long)
public static int java.lang.Long.bitCount(long)
public boolean java.lang.Long.equals(java.lang.Object)
public java.lang.String java.lang.Long.toString()
public static java.lang.String java.lang.Long.toString(long,int)
public static java.lang.String java.lang.Long.toString(long)
public int java.lang.Long.hashCode()
public static long java.lang.Long.reverseBytes(long)
public int java.lang.Long.compareTo(java.lang.Long)
public int java.lang.Long.compareTo(java.lang.Object)
public static java.lang.Long java.lang.Long.getLong(java.lang.String)
public static java.lang.Long java.lang.Long.getLong(java.lang.String,java.lang.Long)
public static java.lang.Long java.lang.Long.getLong(java.lang.String,long)
public byte java.lang.Long.byteValue()
public short java.lang.Long.shortValue()
public int java.lang.Long.intValue()
public long java.lang.Long.longValue()
public float java.lang.Long.floatValue()
public double java.lang.Long.doubleValue()
public static java.lang.Long java.lang.Long.valueOf(long)
public static java.lang.Long java.lang.Long.valueOf(java.lang.String,int) throws java.lang.NumberFormatException
public static java.lang.Long java.lang.Long.valueOf(java.lang.String) throws java.lang.NumberFormatException
public static java.lang.String java.lang.Long.toHexString(long)
public static int java.lang.Long.compare(long,long)
public static java.lang.Long java.lang.Long.decode(java.lang.String) throws java.lang.NumberFormatException
public static long java.lang.Long.reverse(long)
public static long java.lang.Long.highestOneBit(long)
public static long java.lang.Long.lowestOneBit(long)
public static long java.lang.Long.rotateLeft(long,int)
public static long java.lang.Long.rotateRight(long,int)
public static int java.lang.Long.signum(long)
public static java.lang.String java.lang.Long.toBinaryString(long)
public static java.lang.String java.lang.Long.toOctalString(long)
public static long java.lang.Long.parseLong(java.lang.String) throws java.lang.NumberFormatException
public static long java.lang.Long.parseLong(java.lang.String,int) throws java.lang.NumberFormatException
public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
public final void java.lang.Object.wait() throws java.lang.InterruptedException
public final native java.lang.Class java.lang.Object.getClass()
public final native void java.lang.Object.notify()
public final native void java.lang.Object.notifyAll()
2、返回指定公共成员方法:
public long java.lang.Long.longValue()
<span style="color:#555555;">public class ReflectTester {
public Object copy(Object object) throws Exception {
// 获得对象的类型
Class<?> classType = object.getClass();
System.out.println("Class:" + classType.getName());
// 通过默认构造方法创建一个新的对象
</span><span style="color:#ff0000;">Object objectCopy = classType.getConstructor(new Class[]{}).newInstance(new Object[]{});</span><span style="color:#555555;">
// 获得对象的所有属性
Field fields[] = classType.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
Field field = fields[i];
String fieldName = field.getName();
String firstLetter = fieldName.substring(0, 1).toUpperCase();
// 获得和属性对应的getXXX()方法的名字
String getMethodName = "get" + firstLetter + fieldName.substring(1);
// 获得和属性对应的setXXX()方法的名字
String setMethodName = "set" + firstLetter + fieldName.substring(1);
// 获得和属性对应的getXXX()方法
Method getMethod = classType.getMethod(getMethodName, new Class[]{});
// 获得和属性对应的setXXX()方法
Method setMethod = classType.getMethod(setMethodName, new Class[]{field.getType()});
// 调用原对象的getXXX()方法
Object value = getMethod.invoke(object, new Object[]{});
System.out.println(fieldName + ":" + value);
// 调用拷贝对象的setXXX()方法
setMethod.invoke(objectCopy, new Object[]{value});
}
return objectCopy;
}
public static void main(String[] args) throws Exception {
Customer customer = new Customer("Tom", 21);
customer.setId(new Long(1));
Customer customerCopy = (Customer) new ReflectTester().copy(customer);
System.out.println("Copy information:" + customerCopy.getId() + " " + customerCopy.getName() + " "
+ customerCopy.getAge());
}
}
class Customer {
private Long id;
private String name;
private int age;
public Customer() {
}
public Customer(String name, int age) {
this.name = name;
this.age = age;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}</span>
Class:com.langsin.reflection.Customer
id:1
name:Tom
age:21
Copy information:1 Tom 21
Process finished with exit code 0
public class InvokeTester {
public int add(int param1, int param2) {
return param1 + param2;
}
public String echo(String msg) {
return "echo: " + msg;
}
public static void main(String[] args) throws Exception {
Class<?> classType = InvokeTester.class;
Object invokeTester = classType.newInstance();
// Object invokeTester = classType.getConstructor(new
// Class[]{}).newInstance(new Object[]{});
//获取InvokeTester类的add()方法
Method addMethod = classType.getMethod("add", new Class[]{int.class, int.class});
//调用invokeTester对象上的add()方法
Object result = addMethod.invoke(invokeTester, new Object[]{new Integer(100), new Integer(200)});
System.out.println((Integer) result);
//获取InvokeTester类的echo()方法
Method echoMethod = classType.getMethod("echo", new Class[]{String.class});
//调用invokeTester对象的echo()方法
result = echoMethod.invoke(invokeTester, new Object[]{"Hello"});
System.out.println((String) result);
}
}
public class ArrayTester1 {
public static void main(String args[]) throws Exception {
Class<?> classType = Class.forName("java.lang.String");
// 创建一个长度为10的字符串数组
Object array = Array.newInstance(classType, 10);
// 把索引位置为5的元素设为"hello"
Array.set(array, 5, "hello");
// 获得索引位置为5的元素的值
String s = (String) Array.get(array, 5);
System.out.println(s);
}
}
public class ArrayTester2 {
public static void main(String args[]) {
int[] dims = new int[]{5, 10, 15};
//创建一个具有指定的组件类型和维度的新数组。
Object array = Array.newInstance(Integer.TYPE, dims);
Object arrayObj = Array.get(array, 3);
Class<?> cls = arrayObj.getClass().getComponentType();
System.out.println(cls);
arrayObj = Array.get(arrayObj, 5);
Array.setInt(arrayObj, 10, 37);
int arrayCast[][][] = (int[][][]) array;
System.out.println(arrayCast[3][5][10]);
}
}
public class RefFiled {
public double x;
public Double y;
public static void main(String args[]) throws NoSuchFieldException, IllegalAccessException {
Class c = RefFiled.class;
Field xf = c.getField("x");
Field yf = c.getField("y");
RefFiled obj = new RefFiled();
System.out.println("变更前x=" + xf.get(obj));
//变更成员x值
xf.set(obj, 1.1);
System.out.println("变更后x=" + xf.get(obj));
System.out.println("变更前y=" + yf.get(obj));
//变更成员y值
yf.set(obj, 2.1);
System.out.println("变更后y=" + yf.get(obj));
}
}