反射...

一、反射的定义

二、获取Class对象三种方式

全类名：包名+类名。

public class test {public static void main(String [] args) throws ClassNotFoundException  {//第一种方式Class class1=Class.forName("test02.Student");//第二种方法Class class2=Student.class;//第三种方法Student student=new Student();Class class3=student.getClass();System.out.println(class1==class2);System.out.println(class2==class3);System.out.println(class1);}
}

三、利用反射获取构造方法

public class test {public static void main(String [] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException  {//获取class字节码对象文件Class class1=Class.forName("test02.Student");//获取所有构造方法Constructor[] css=class1.getDeclaredConstructors();for(Constructor c:css) {System.out.println(c);}System.out.println("-------------");//获取单个构造方法Constructor con1= class1.getDeclaredConstructor(String.class);System.out.println(con1);}
}

public class Student {
private String name;
private int age;
public Student() {}
public Student(String name) {this.setName(name);
}
protected Student(String name,int age) {this.setName(name);this.setAge(age);
}
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;
}
@Override
public String toString() {return "Student [name=" + name + ", age=" + age + "]";
}}

四、利用反射获取成员变量

public class Student {
private String name;
private int age;
public Student() {}
public Student(String name,int age) {this.setName(name);this.setAge(age);
}
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;
}
@Override
public String toString() {return "Student [name=" + name + ", age=" + age + "]";
}}

public class test {public static void main(String [] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException {//获取class字节码对象文件Class class1=Class.forName("test02.Student");//获取所有成员变量Field[] fi= class1.getDeclaredFields();for(Field f:fi) {System.out.println(f);}System.out.println("--------------");//获取单个成员变量Field fii= class1.getDeclaredField("name");System.out.println(fii);Student s=new Student("zhangsan",23);fii.setAccessible(true);Object r= fii.get(s);System.out.println(r);}
}

五、利用反射获取成员方法

public class Student {
private String name;
private int age;
public Student() {}
public Student(String name,int age) {this.setName(name);this.setAge(age);
}
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;
}
public void eat(String something) {System.out.println("在吃"+something);
}
@Override
public String toString() {return "Student [name=" + name + ", age=" + age + "]";
}}

public class test {public static void main(String [] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {//获取class字节码对象文件Class class1=Class.forName("test02.Student");//获取指定的成员方法Method method= class1.getDeclaredMethod("eat", String.class);System.out.println(method);//创建对象Student s=new Student();method.invoke(s, "汉堡");}
}

六、综合练习

练习1：信息保存

对于任意一个对象，都可以把对象所有的字段名和值，保存到文件中去。

分析：可以利用反射，将成员变量获取出来，再利用IO流将获取出来的变量，写入文件中。

Student类：

public class Student {private String name;private int age;private String gender;private double height;private String hobby;public Student() {}public Student(String name,int age,String gender,double height,String hobby) {this.setName(name);this.setAge(age);this.setGender(gender);this.setHeight(height);this.setHobby(hobby);}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;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}public String getHobby() {return hobby;}public void setHobby(String hobby) {this.hobby = hobby;}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + ", gender=" + gender + ", height=" + height + ", hobby="+ hobby + "]";}}

Teacher类：

public class Teacher {
private String name;
private int salary;
public Teacher() {}
public Teacher(String name,int salary) {this.setName(name);this.setSalary(salary);
}
public String getName() {return name;
}
public void setName(String name) {this.name = name;
}
public int getSalary() {return salary;
}
public void setSalary(int salary) {this.salary = salary;
}
@Override
public String toString() {return "Teacher [name=" + name + ", salary=" + salary + "]";
}
}

测试类：

package test02;import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Field;public class test {public static void main(String [] args) throws IllegalArgumentException, IllegalAccessException, IOException{Student s=new Student("李明",23,"女",92.5,"画画");Teacher t=new Teacher("王老师",8500);Get(s);}//创建一个方法获取成员变量public static void Get(Object obj) throws IllegalArgumentException, IllegalAccessException, IOException {//Object是获取对象//获取字节码文件Class cla=obj.getClass();//创建IO流BufferedWriter bw=new BufferedWriter(new FileWriter("c.txt"));//获取每个成员变量Field[] fields=cla.getDeclaredFields();//利用循环获取成员变量for(Field field:fields) {field.setAccessible(true);String name=field.getName();Object vaule= field.get(obj);bw.write(name+"="+vaule);bw.newLine();}bw.close();}
}