反射的案例-蒲公英云

1.反射获取构造方法并使用练习1【应用】

案例需求
- 通过反射获取公共的构造方法并创建对象

代码实现

学生类

public class Student {

//成员变量：一个私有，一个默认，一个公共
private String name;
int age;
public String address;
//构造方法：一个私有，一个默认，两个公共
public Student() {
}
private Student(String name) {
    this.name = name;
}
Student(String name, int age) {
    this.name = name;
    this.age = age;
}
public Student(String name, int age, String address) {
    this.name = name;
    this.age = age;
    this.address = address;
}
//成员方法：一个私有，四个公共
private void function() {
    System.out.println("function");
}
public void method1() {
    System.out.println("method");
}
public void method2(String s) {
    System.out.println("method:" + s);
}
public String method3(String s, int i) {
    return s + "," + i;
}
@Override
public String toString() {
    return "Student{" +
            "name='" + name + '\'' +
            ", age=" + age +
            ", address='" + address + '\'' +
            '}';
}

}

测试类

public class ReflectDemo02 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        //获取Class对象
        Class<?> c = Class.forName("com.itheima_02.Student");
        //public Student(String name, int age, String address)
        //Constructor<T> getConstructor(Class<?>... parameterTypes)
        Constructor<?> con = c.getConstructor(String.class, int.class, String.class);
        //基本数据类型也可以通过.class得到对应的Class类型
        //T newInstance(Object... initargs)
        Object obj = con.newInstance("林青霞", 30, "西安");
        System.out.println(obj);
    }
}

2.反射获取构造方法并使用练习2【应用】

案例需求
- 通过反射获取私有构造方法并创建对象

代码实现

学生类：参见上方学生类
测试类

public class ReflectDemo03 {

public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    //获取Class对象
    Class<?> c = Class.forName("com.itheima_02.Student");
    //private Student(String name)
    //Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)
    Constructor<?> con = c.getDeclaredConstructor(String.class);
    //暴力反射
    //public void setAccessible(boolean flag):值为true，取消访问检查
    con.setAccessible(true);
    Object obj = con.newInstance("林青霞");
    System.out.println(obj);
}

}

3.反射获取成员变量并使用练习【应用】

案例需求
- 通过反射获取成员变量并赋值

代码实现

学生类：参见上方学生类
测试类

public class ReflectDemo02 {

public static void main(String[] args) throws Exception {
    //获取Class对象
    Class<?> c = Class.forName("com.itheima_02.Student");
    //Student s = new Student();
    Constructor<?> con = c.getConstructor();
    Object obj = con.newInstance();
    System.out.println(obj);
    //s.name = "林青霞";

// Field nameField = c.getField(“name”); //NoSuchFieldException: name

    Field nameField = c.getDeclaredField("name");
    nameField.setAccessible(true);
    nameField.set(obj, "林青霞");
    System.out.println(obj);
    //s.age = 30;
    Field ageField = c.getDeclaredField("age");
    ageField.setAccessible(true);
    ageField.set(obj,30);
    System.out.println(obj);
    //s.address = "西安";
    Field addressField = c.getDeclaredField("address");
    addressField.setAccessible(true);
    addressField.set(obj,"西安");
    System.out.println(obj);
}

}

4.反射获取成员方法并使用练习【应用】

案例需求
- 通过反射获取成员方法并调用

代码实现

学生类：参见上方学生类
测试类

public class ReflectDemo02 {

public static void main(String[] args) throws Exception {
    //获取Class对象
    Class<?> c = Class.forName("com.itheima_02.Student");
    //Student s = new Student();
    Constructor<?> con = c.getConstructor();
    Object obj = con.newInstance();
    //s.method1();
    Method m1 = c.getMethod("method1");
    m1.invoke(obj);
    //s.method2("林青霞");
    Method m2 = c.getMethod("method2", String.class);
    m2.invoke(obj,"林青霞");

// String ss = s.method3(“林青霞”,30);
// System.out.println(ss);

    Method m3 = c.getMethod("method3", String.class, int.class);
    Object o = m3.invoke(obj, "林青霞", 30);
    System.out.println(o);
    //s.function();

// Method m4 = c.getMethod(“function”); //NoSuchMethodException: com.itheima_02.Student.function()

    Method m4 = c.getDeclaredMethod("function");
    m4.setAccessible(true);
    m4.invoke(obj);
}

}

5.反射练习之越过泛型检查

案例需求
- 通过反射技术，向一个泛型为Integer的集合中添加一些字符串数据
代码实现

public class ReflectTest01 {

public static void main(String[] args) throws Exception {
    //创建集合
    ArrayList<Integer> array = new ArrayList<Integer>();

// array.add(10);
// array.add(20);
// array.add(“hello”);

    Class<? extends ArrayList> c = array.getClass();
    Method m = c.getMethod("add", Object.class);
    m.invoke(array,"hello");
    m.invoke(array,"world");
    m.invoke(array,"java");
    System.out.println(array);
}

}

6.运行配置文件中指定类的指定方法

案例需求
- 通过反射运行配置文件中指定类的指定方法

代码实现

public class ReflectTest02 {

public static void main(String[] args) throws Exception {
    //加载数据
    Properties prop = new Properties();
    FileReader fr = new FileReader("myReflect\\class.txt");
    prop.load(fr);
    fr.close();
    /*
        className=com.itheima_06.Student
        methodName=study
     */
    String className = prop.getProperty("className");
    String methodName = prop.getProperty("methodName");
    //通过反射来使用
    Class<?> c = Class.forName(className);//com.itheima_06.Student
    Constructor<?> con = c.getConstructor();
    Object obj = con.newInstance();
    Method m = c.getMethod(methodName);//study
    m.invoke(obj);
}