黑马程序员—反射篇

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1：获取字节码的三种方式： Employee emp=new Employee();
Class clazz1=Employee.class;
Class clazz2=Class.forName(“java.util.HashSet”);
Class clazz3=emp.getClass();
2:通过字节码获取对象:
Employee enp=(Employee) clazz2.newInstance();
3:通过字节码获取字段：
Field [] field=clazz2.getDeclaredFields(); 遍历数组
for(Field f : field) {}
f.setAccessible(true); 允许取私有属性的值
f.type(); 先判断字段的数据类型
f.get(emp); 获取字段的值
f.set(“olaValue”,”newValue”);
4:通过字节码获取方法调用方法：
第一个参数：方法名字 第二个参数：数据类型
Method method=clazz2.getMethod(“main”,String[].class);
执行方法 ，第一个参数，底层方法为静态可以为null,
第二个参数：是执行这个方法所需要的参数
method.invoke(null,new Object[]{“”,”“,”“});

package com.itheima.org1;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collection;
import java.util.Properties;

/**
 * @author myluo
 *  字节码的获取和类型判断
 *  反射就是把java类的各个部分映射成新的Java类
 */
public class ReflectTest1 {
                    public static void main(String[] args)   throws   Exception {
                                 //  reflectMethod1();
                                  // reflevtMethod2();
                                  // reflectMethod3();
                                  //   reflectMethod4();
                                  //   reflectMethod5(args[0]);
                                   //    reflectMethod6();
                                    //   reflectArrays();   
                                         reflectArrayList();
                    }

                    //反射集合,HashSet  不能重复， ArrayList可以重复
                    private static void reflectArrayList() throws IOException, ClassNotFoundException, InstantiationException, IllegalAccessException {
                        // TODO Auto-generated method stub
                        //读取配置文件
                        InputStream   is=new   FileInputStream(new  File("array.properties"));

                        Properties  pro=new  Properties();

                        //把流加载到pro对象
                        pro.load(is);
                        is.close();

                        String   className=pro.getProperty("className");

                        System.out.println(className);
                        //创建Collection对象
                        Collection coll=(Collection)Class.forName(className).newInstance();

                        ReflectPoint   a1=new  ReflectPoint(1,1);
                        ReflectPoint   a2=new  ReflectPoint(5,5);
                        ReflectPoint   a3=new  ReflectPoint(1,1);

                        coll.add(a1);
                        coll.add(a2);
                        coll.add(a3);
                        coll.add(a1);


                        System.out.println(coll.size());

                    }


                    //反射数组clazz.isArray()是否是数组Array.getLength(str);获取数组的长度
                    private static void reflectArrays() {
                        // TODO Auto-generated method stub

                               String  []   str=new  String[]{"爬山","游泳","跑步"};

                             //   String   str="xxxx";
                               Class   clazz=  str.getClass();

                               //判断是否是数组
                               if(clazz.isArray()){
                                           //获取对象的长度
                                          int   len=  Array.getLength(str);
                                          for(int  i=0;i<len;i++){
                                                 //根据对象下标获取数组的值
                                                 System.out.println(Array.get(str, i)); 
                                          }
                               }else{
                                    System.out.println(str);
                               }

                    }

                    //只要是数组里面是基本数据类型的数组，就不能转换成Object[]数组
                    private static void reflectMethod6() {
                        // TODO Auto-generated method stub
                             int   []  a1=new  int[]{1,2,3};
                             int  []  a2=new  int[2];
                             int  [][]a3=new  int [][]{
                                     {1,2,1},
                                     {3,4,5}
                             };
                             String  []  a4=new  String[]{"jack","456"};
                             //数据类型一样他们的字节码是相等的
                             System.out.println(a1.getClass()==a2.getClass());
                            Object   obj1=a1;
                            Object   obj2=a2;
                            Object   obj3=a3;
                            Object   obj4=a4;
                            //只要是数组里面是基本数据类型的数组，就不能转换成Object[]数组
                            //Object []  objec1=a1;    //int.class
                            //Object []  objec1=a2;   //int.class
                            Object []  objec1=a3;   //int[].class
                            Object []  objec4=a4;   //String.class


                            System.out.println(a1.getClass().getName());
                            System.out.println(a1.getClass().getSuperclass().getName());
                            System.out.println(a2.getClass().getSuperclass().getName());
                            System.out.println(a3.getClass().getSuperclass().getName());
                            System.out.println(a4.getClass().getSuperclass().getName());

                            //数组转换成list集合asList
                            //System.out.println(Arrays.asList(a1));
                            System.out.println(Arrays.asList(a4));



                    }

                    //反射获取方法（其他类的）main方法
                    private static void reflectMethod5(String  args) throws InstantiationException, IllegalAccessException, ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
                        // TODO Auto-generated method stub
                                 // Class   clazz= ReflectPoint.class;
                               //   ReflectPoint  rp= (ReflectPoint)clazz.newInstance();
                                 // String.class.getMethod(arg0, arg1);
                          //调用main方法,
                         //  MainReflect.main(new  String[]{"123","456","789","555"});
                           //com.itheima.org1.MainReflect
                          System.out.println("编译是传进来的包名："+args);
                           //根据反射的包名获取字节码,得到method类
                           Method  method= Class.forName(args).getMethod("main", String[].class);

                           //调用main方法
                           method.invoke(null, new  Object[]{new  String[]{"张三","李四","王五"}});

                    }

                    //反射修改对象字段的值
                    private static void reflectMethod4() throws InstantiationException, IllegalAccessException {
                        // TODO Auto-generated method stub
                              //加载字节码
                              Class   clazz= ReflectPoint.class;
                              //获取对象
                             ReflectPoint   rp=(ReflectPoint) clazz.newInstance();
                              //获取所有字段
                             Field [] field=clazz.getDeclaredFields();
                             //遍历数组
                             for(Field   f : field ){
                                        //允许私有
                                       f.setAccessible(true);

                                        if (f.getType()==String.class) {
                                                    //获取对象的字段值
                                                    System.out.println(f.get(rp));
                                                    String str = (String) f.get(rp);
                                                    //替换e为A
                                                    f.set(rp, str.replace("e", "A"));
                                                    System.out.println(f.get(rp));
                                        }
                             }

                             System.out.println("=========================");
                             System.out.println(rp);
                    }


                    //反射的字段  ，field
                    private static void reflectMethod3() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
                        // TODO Auto-generated method stub

                                ReflectPoint   rp1=new  ReflectPoint(5,8);
                                ReflectPoint   rp2=new  ReflectPoint(2,3);
                                //加载字节码
                                Class   clazz=rp1.getClass();

                                //获取（指定名字）的字段的(公有属性的)属性
                                Field    filedy=clazz.getField("y");

                                //获取（自定对象）字段的值
                               Object   y= filedy.get(rp1);

                               System.out.println("y的值="+y);

                               //获取是有(不管是私有)属性
                              Field   fieldx= clazz.getDeclaredField("x");
                              //允许获取私有属性的值
                              fieldx.setAccessible(true);
                               //获取字段的值
                               Object   x=fieldx.get(rp2);

                               System.err.println("x的值="+x);

                    }

                    //映射Java类中构造函数
                    private static void reflevtMethod2() throws NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
                        // TODO Auto-generated method stub
                                 //加载字节码
                                Class  clazz= String.class;

                                //获取指定类型（StringBuffered）构造函数
                                Constructor     constructor=clazz.getConstructor(StringBuffer.class);

                                //根据构造函数获取对象
                                 String    str= (String) constructor.newInstance(new  StringBuffer("abc"));

                                 //打印一下对象
                                 System.out.println(str.charAt(1));

                    }


                    //字节码的三种创建方式
                    private static void reflectMethod1()
                            throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
                        String   str1="abc";
                           //字节码一
                           Class   clazz1=str1.getClass();
                           //字节码二
                           Class  clazz2=String.class;
                           //字节码三
                          Class  clazz3= Class.forName("java.lang.String");
                          //true
                          System.out.println(clazz1==clazz2);
                          //true
                          System.out.println(clazz1==clazz3);

                          //判断是否是基本数据类型  false
                          System.out.println(clazz1.isPrimitive());

                          //判断int是否是基本数据类型  true
                          System.out.println(int.class.isPrimitive());


                          //判断int字节码是否和Integer字节码是否相等,false
                          System.out.println(int.class==Integer.class);

                          //判断int类型是否等于Integer的类型  ,true
                          System.out.println(int.class==Integer.TYPE);

                          //判断数组是否是基本数据类型,false
                          System.out.println(int[].class.isPrimitive());

                          //判断是否是数组,true
                          System.out.println(int[].class.isArray());

                         //获取方法 
                         Method   method= String.class.getMethod("charAt", int.class);

                         System.out.println("method="+method.invoke(str1, 2));

                    }
}



class   MainReflect  {
               public static void main(String[] args) {
                               for(String   str :  args){
                                             System.out.println(str);
                               }
            }
}


//反射的类
class   ReflectPoint   {

                  private   int  x;
                  public    int  y;
                  public    String  str1="itheima";
                  public    String  str2="reflect";
                  public    String  str3="red";
                public ReflectPoint(int x, int y) {

                    this.x = x;
                    this.y = y;
                }

                public ReflectPoint() {
                    super();
                }


                @Override
                public int hashCode() {
                    final int prime = 31;
                    int result = 1;
                    result = prime * result + x;
                    result = prime * result + y;
                    return result;
                }

                @Override
                public boolean equals(Object obj) {
                    if (this == obj)
                        return true;
                    if (obj == null)
                        return false;
                    if (getClass() != obj.getClass())
                        return false;
                    ReflectPoint other = (ReflectPoint) obj;
                    if (x != other.x)
                        return false;
                    if (y != other.y)
                        return false;
                    return true;
                }

                public  String   toString(){
                    return   "str1="+str1+"str2="+str2+"str3="+str3;
                }

}