java反射学习(1):反射的基本操作

一 用class.forname反射获取对象(必须要一个无参的构造函数)

package com.learing._01;class Student{ public Student(){ System.out.println("Student类的构造方法"); }  @Override public String toString(){ return "Student类的toString()方法"; }}public class ReflectDemo {public static void main(String args[]) throws Exception{Class<?> cls = Class.forName("com.learing._01.Student");Object obj = cls.newInstance();}}

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二 获取构造方法

package com.learing._01;import java.lang.reflect.Constructor;public class ReflectStringDemo { public static void main(String args[]) throws Exception{Class<?> cls = Class.forName("java.lang.String");Constructor<?> cons[] = cls.getConstructors();for(int i = 0 ; i < cons.length ; i++){System.out.println(cons[i]);}}}

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三 通过构造方法实例化对象

package com.learing._01;import java.lang.reflect.Constructor;class Student {private String name;private Integer age;public Student(String name, Integer age) {this.name = name;this.age = age;}public Student() {}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + "]";}}public class ReflectDemo {public static void main(String args[]) throws Exception {Class<?> cls = Class.forName("com.learing._01.Student");Constructor<?> cons = cls.getConstructor(String.class,Integer.class);Object obj = cons.newInstance("SMITH",20);System.out.println(obj.toString());}}

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四 通过反射获取方法

此功能用于IDE开发工具,当输入一“.”时候,会出来该类有哪些方法

package com.learing._01;import java.lang.reflect.Constructor;import java.lang.reflect.Method;import java.lang.reflect.Modifier;interface Message{public void get();}class Student implements Message{@Overridepublic void get() {}public void print(String name,int age){}public void fun() throws Exception{}}public class ReflectDemo {public static void main(String args[]) throws Exception {Class<?> cls = Class.forName("com.learing._01.Student");Method met[] = cls.getMethods();for(int i = 0 ; i < met.length ; i++){//以下 partA的输出和partB一样// partA//System.out.println(met[i]);// partB startSystem.out.print(Modifier.toString(met[i].getModifiers())+" ");//得到修饰符 public final nativeSystem.out.print(met[i].getReturnType().getSimpleName()+" ");//得到返回类型  voidSystem.out.print(met[i].getName()+"("); // 得到方法名 get,printClass<?> params[] = met[i].getParameterTypes(); //得到方法的参数类型if(params!=null&¶ms.length > 0 ){for(int j = 0 ; j < params.length ; j++){System.out.print(params[j].getSimpleName()+""); //取参数if(j<params.length-1){System.out.print(" , ");}}}System.out.print(") ");Class<?> exceps[] =  met[i].getExceptionTypes(); //获取异常if( exceps!=null && exceps.length>0 ){System.out.print(" throws ");for(int j = 0 ; j < exceps.length ; j++){System.out.print(exceps[j].getSimpleName());if(j < exceps.length -1){System.out.print(", ");}}}System.out.println();// partB end}}}

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五 反射调用方法

package com.learing._01;import java.lang.reflect.Constructor;import java.lang.reflect.Method;import java.lang.reflect.Modifier;class Student{private String name;public void setName(String name){this.name = name;}public String getName(){return name;}}public class ReflectDemo {public static void main(String args[]) throws Exception{Class<?> cls = Class.forName("com.learing._01.Student");Object obj = cls.newInstance(); //实例化对象Method setNameMethod = cls.getMethod("setName", String.class);Method getNameMethod = cls.getMethod("getName");setNameMethod.invoke(obj, "SMITH"); // 对象.setName("SMITH");System.out.println(getNameMethod.invoke(obj));}}

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六 属性操作

package com.learing._01;import java.lang.reflect.Constructor;import java.lang.reflect.Field;import java.lang.reflect.Method;import java.lang.reflect.Modifier;interface Message{ public static final String INFO = "hello world";}class Person{private String name;private Integer age;}class Student extends Person implements Message{private String school;private Double price;}public class ReflectDemo {public static void main(String args[]) throws Exception{Class<?> cls = Class.forName("com.learing._01.Student");{ //取得继承而来的全部属性System.out.println();Field fields[] = cls.getFields();System.out.println("继承而来的属性");for(int i = 0 ; i <  fields.length ; i++){System.out.println(fields[i]);}}{//取得本类定义的全部属性System.out.println();Field fields[] = cls.getDeclaredFields();System.out.println("本类定义的全部属性");for(int i = 0 ; i <  fields.length ; i++){System.out.println(fields[i]);}}{//取得父类属性System.out.println();Field fields[] = cls.getSuperclass().getDeclaredFields(); System.out.println("父类属性定义的全部属性");for(int i = 0 ; i <  fields.length ; i++){System.out.println(fields[i]);}}{  //操作属性  System.out.println();  System.out.println("属性的操作");  Object obj = cls.newInstance();  Field schoolField = cls.getDeclaredField("school");  schoolField.setAccessible(true);//以为school属性为private ,setAccessible可以操作该属性  schoolField.set(obj,"清华大学");  System.out.println(schoolField.get(obj));}}}

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