JAVA 私塾笔记整理——反射机制(Reflection)
JAVA 私塾笔记整理——反射机制(Reflection)一.反射是什么？
反射它允许运行中的 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。
二.分析类的构成？
1.获取Class对象：
Class c = Class.forName("java.lang.String");
Class c = int.class;
Class c = Integer.TYPE;
*它们可获得基本类型的类信息。其中后一种方法中访问的是基本类型的封装类 (如Integer) 中预先定义好的 TYPE 字段。
2.获取类的方法
package cn;
import java.lang.reflect.*;
public class Test {
∵ 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("cn.Test");
Method methlist[] = cls.getDeclaredMethods();
for (int i = 0; i < methlist.length; i++) {
Method m = methlist;
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);
Class evec[] = m.getExceptionTypes();
for (int j = 0; j < evec.length; j++)
System.out.println("exc #" + j + " " + evec);
System.out.println("return type = " + m.getReturnType());
System.out.println("-----");
}
} catch (Throwable e) {
System.err.println(e);
}
}
}输出的结果如下：
name = f1
decl class = class cn.Test
param #0 class java.lang.Object
param #1 int
exc #0 class java.lang.NullPointerException
return type = int
-----
name = main
decl class = class cn.Test
param #0 class [Ljava.lang.String;
return type = void
-----
3. 获取构造器
package cn;
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("cn.Test");
Constructor ctorlist[] = cls.getDeclaredConstructors();
for (int i = 0; i < ctorlist.length; i++) {
Constructor ct = ctorlist;
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);
Class evec[] = ct.getExceptionTypes();
for (int j = 0; j < evec.length; j++)
System.out.println("exc #" + j + " " + evec);
System.out.println("-----");
}
} catch (Throwable e) {
System.err.println(e);
}
}
}这个程序运行的结果是：
name = cn.Test
decl class = class cn.Test
-----
name = cn.Test
decl class = class cn.Test
param #0 int
param #1 double
-----
4. 获取类的属性字段（域字段）
package cn;
import java.lang.reflect.*;
public class Test {
∵ double d;
public static final int i = 37;
String s = "testing";
public static void main(String args[]) {
try {
Class cls = Class.forName("cn.Test");
Field fieldlist[] = cls.getDeclaredFields();
for (int i = 0; i < fieldlist.length; i++) {
Field fld = fieldlist;
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);
}
}
}这个程序的输出是：
name = d
decl class = class cn.Test
type = double
modifiers = ∵
-----
name = i
decl class = class cn.Test
type = int
modifiers = public static final
-----
name = s
decl class = class cn.Test
type = class java.lang.String
modifiers =
-----
三.如何动态调用
（要动态调用就要创建实例）
Class cls = Class.forName("cn.Test");
Object obj = cls.newInstance();
*使用反射机制的主流框架都是默认调用无参的public构造器，所以我们不能改类的构造器。
四.设计实现javaBean功能
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
public class JavaBean {
∵ static ObjectmyJavaBean(Map map,Class cls) throws Exception{
//得到类中所有字段
Field fs[] = cls.getDeclaredFields();
//new 一个实例
Object obj = cls.newInstance();
for(int i=0;i<fs.length;i++){
//得到字段名
Object v = map.get(fs.getName());
if(v!=null){
//只有一个参数
Class partypes[] = new Class;
partypes = fs.getType();
//拼setter方法
Method meth = cls.getMethod("set"
+ fs.getName().substring(0,1).toUpperCase()
+ fs.getName().substring(1), partypes);
Object arglist[] = new Object;
arglist = v;
meth.invoke(obj, arglist);
}
}
return obj;
}
public static void main(String[] args) throws Exception {
Map map = new HashMap();
map.put("userId", "1234");
map.put("name", "4321");
map.put("ddd", "dddd dddd");
Object obj = myJavaBean(map,AModel.class);
AModel am = (AModel)obj;
System.out.println("am.userId=" + am.getUserId() + ",name=" + am.getName());
}
}
class AModel{
∵ String userId,name;
public String getUserId() {
return userId;
}
public void setUserId(String userId) {
this.userId = userId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}这个程序的输出是：
am.userId=1234,name=4321
JAVA 私塾经典学习视频，可以到官网下载观看，w ww.javass.cn
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