文章目录
认识反射、获取类
反射是什么？
反射学什么？
反射第一步：加载类，获取字节码：Class对象
Student
java
public class Student {
private String name;
private int age;
private char sex;
private double height;
private String hobby;
public Student() {
}
public Student(String name, int age, char sex, double height, String hobby) {
this.name = name;
this.age = age;
this.sex = sex;
this.height = height;
this.hobby = 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 char getSex() {
return sex;
}
public void setSex(char sex) {
this.sex = sex;
}
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;
}
}**Test1Class **
java
/**
* 目标：获取Class对象。
*/
public class Test1Class {
public static void main(String[] args) throws Exception {
Class c1 = Student.class;
System.out.println(c1.getName()); // 全类名(包名+类名)
System.out.println(c1.getSimpleName()); // 简名：Student
Class c2 = Class.forName("com.wuxuan.Junit_reflect_annotation_proxy_app.d2_reflect.Student");//填全类名
System.out.println(c1 == c2);
Student s = new Student();
Class c3 = s.getClass();
System.out.println(c3 == c2);
}
}总结
获取类的构造器
Cat
java
public class Cat {
public static int a;
public static final String COUNTRY = "中国";
private String name;
private int age;
public Cat(){
System.out.println("无参数构造器执行了~~");
}
private Cat(String name, int age) {
System.out.println("有参数构造器执行了~~");
this.name = name;
this.age = age;
}
private void run(){
System.out.println("🐱跑的贼快~~");
}
public void eat(){
System.out.println("🐱爱吃猫粮~");
}
private String eat(String name){
return "🐱最爱吃:" + name;
}
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 "Cat{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}**Test2Constructor **
java
/**
* 目标：掌握获取类的构造器，并对其进行操作。
*/
public class Test2Constructor {
@Test
public void testGetConstructors(){
// 1、反射第一步：必须先得到这个类的Class对象
Class c = Cat.class;
// 2、获取类的全部构造器
// Constructor[] constructors = c.getConstructors();
Constructor[] constructors = c.getDeclaredConstructors();
// 3、遍历数组中的每个构造器对象
for (Constructor constructor : constructors) {
System.out.println(constructor.getName() + "--->"
+ constructor.getParameterCount());
}
}
@Test
public void testGetConstructor() throws Exception {
// 1、反射第一步：必须先得到这个类的Class对象
Class c = Cat.class;
// 2、获取类的某个构造器：无参数构造器
Constructor constructor1 = c.getDeclaredConstructor();
System.out.println(constructor1.getName() + "--->"
+ constructor1.getParameterCount());
constructor1.setAccessible(true); // 禁止检查访问权限
Cat cat = (Cat) constructor1.newInstance();
System.out.println(cat);
AtomicInteger a;
// 3、获取有参数构造器
Constructor constructor2 =
c.getDeclaredConstructor(String.class, int.class);
System.out.println(constructor2.getName() + "--->"
+ constructor2.getParameterCount());
constructor2.setAccessible(true); // 禁止检查访问权限
Cat cat2 = (Cat) constructor2.newInstance("叮当猫", 3);
System.out.println(cat2);
}
}
获取类的成员变量
Cat
java
public class Cat {
public static int a;
public static final String COUNTRY = "中国";
private String name;
private int age;
public Cat(){
System.out.println("无参数构造器执行了~~");
}
private Cat(String name, int age) {
System.out.println("有参数构造器执行了~~");
this.name = name;
this.age = age;
}
private void run(){
System.out.println("🐱跑的贼快~~");
}
public void eat(){
System.out.println("🐱爱吃猫粮~");
}
private String eat(String name){
return "🐱最爱吃:" + name;
}
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 "Cat{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}**Test3Field **
java
/**
* 目标：掌握获取类的成员变量，并对其进行操作。
*/
public class Test3Field {
@Test
public void testGetFields() throws Exception {
// 1、反射第一步：必须是先得到类的Class对象
Class c = Cat.class;
// 2、获取类的全部成员变量。
Field[] fields = c.getDeclaredFields();
// 3、遍历这个成员变量数组
for (Field field : fields) {
System.out.println(field.getName() + "---> "+ field.getType());
}
// 4、定位某个成员变量
Field fName = c.getDeclaredField("name");
System.out.println(fName.getName() + "--->" + fName.getType());
Field fAge = c.getDeclaredField("age");
System.out.println(fAge.getName() + "--->" + fAge.getType());
// 赋值
Cat cat = new Cat();
fName.setAccessible(true); // 禁止访问控制权限
fName.set(cat, "卡菲猫");
System.out.println(cat);
// 取值
String name = (String) fName.get(cat);
System.out.println(name);
}
}
获取类的成员方法
Cat
java
public class Cat {
public static int a;
public static final String COUNTRY = "中国";
private String name;
private int age;
public Cat(){
System.out.println("无参数构造器执行了~~");
}
private Cat(String name, int age) {
System.out.println("有参数构造器执行了~~");
this.name = name;
this.age = age;
}
private void run(){
System.out.println("🐱跑的贼快~~");
}
public void eat(){
System.out.println("🐱爱吃猫粮~");
}
private String eat(String name){
return "🐱最爱吃:" + name;
}
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 "Cat{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}Test4Method
java
/**
* 目标：掌握获取类的成员方法，并对其进行操作。
*/
public class Test4Method {
@Test
public void testGetMethods() throws Exception {
// 1、反射第一步：先得到Class对象。
Class c = Cat.class;
// 2、获取类的全部成员方法。
Method[] methods = c.getDeclaredMethods();
// 3、遍历这个数组中的每个方法对象
for (Method method : methods) {
System.out.println(method.getName() + "--->"
+ method.getParameterCount() + "---->"
+ method.getReturnType());
}
// 4、获取某个方法对象
Method run = c.getDeclaredMethod("run"); // 拿run方法，无参数的
System.out.println(run.getName() + "--->"
+ run.getParameterCount() + "---->"
+ run.getReturnType());
Method eat = c.getDeclaredMethod("eat", String.class);
System.out.println(eat.getName() + "--->"
+ eat.getParameterCount() + "---->"
+ eat.getReturnType());
Cat cat = new Cat();
run.setAccessible(true); // 禁止检查访问权限
Object rs = run.invoke(cat); // 调用无参数的run方法，用cat对象触发调用的。
System.out.println(rs);
eat.setAccessible(true); // 禁止检查访问权限
String rs2 = (String) eat.invoke(cat, "鱼儿");
System.out.println(rs2);
}
}
作用、应用场景
Student
java
public class Student {
private String name;
private int age;
private char sex;
private double height;
private String hobby;
public Student() {
}
public Student(String name, int age, char sex, double height, String hobby) {
this.name = name;
this.age = age;
this.sex = sex;
this.height = height;
this.hobby = 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 char getSex() {
return sex;
}
public void setSex(char sex) {
this.sex = sex;
}
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;
}
}**Teacher **
java
public class Teacher {
private String name;
private double salary;
public Teacher() {
}
public Teacher(String name, double salary) {
this.name = name;
this.salary = salary;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}**ObjectFrame **
java
public class ObjectFrame {
// 目标：保存任意对象的字段和其数据到文件中去
public static void saveObject(Object obj) throws Exception {
PrintStream ps = new PrintStream(new FileOutputStream("D:\\Code\\JDBC\\Basic\\src\\main\\java\\com\\wuxuan\\Junit_reflect_annotation_proxy_app\\d2_reflect\\data.txt", true));
// obj是任意对象，到底有多少个字段要保存。
Class c = obj.getClass();
String cName = c.getSimpleName();
ps.println("---------------" + cName + "------------------------");
// 2、从这个类中提取它的全部成员变量
Field[] fields = c.getDeclaredFields();
// 3、遍历每个成员变量。
for (Field field : fields) {
// 4、拿到成员变量的名字
String name = field.getName();
// 5、拿到这个成员变量在对象中的数据。
field.setAccessible(true); // 禁止检查访问控制
String value = field.get(obj) + "";
ps.println(name + "=" + value);
}
ps.close();
}
}**Test5Frame **
java
/**
* 目标：使用反射技术：设计一个保存对象的简易版框架。
*/
public class Test5Frame {
@Test
public void save() throws Exception {
Student s1 = new Student("黑马吴彦祖", 45, '男', 185.3, "蓝球，冰球，阅读");
Teacher t1 = new Teacher("播妞", 999.9);
// 需求：把任意对象的字段名和其对应的值等信息，保存到文件中去。
ObjectFrame.saveObject(s1);
ObjectFrame.saveObject(t1);
}
}
