反射¶

概念¶

反射机制将类的各个组成部分封装为其他对象。

优点¶

可以在程序运行过程中，操作这些对象
可以解耦，提高程序的可扩展性

举例¶

Class personClass = Person.class;

Field[] fields = personClass.getFields();
for (Field field : fields) {
    System.out.println(field);
}

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

Field[] declaredFields = personClass.getDeclaredFields();
for (Field declaredField : declaredFields) {
    System.out.println(declaredFields);
}

Class对象的功能¶

获取功能¶

成员变量

Field[] getFields();
Field getField(String name);
Field[] getDeclaredFields(); // 不考虑修饰符
Field getDeclaredField(String name);

构造方法

Constructor<?>[] getConstructors();
Constructor<T> getConstructor(类<?>... parameterTypes);
Constructor<T> getDeclaredConstructor(类<?>... parameterTypes);
Constructor<?>[] getDeclaredConstructors();

成员方法

Method[] getMethods();
Method getMethod(String name, 类<?>... parameterTypes);
Method[] getDeclaredMethods();
Method getDeclaredMethod(String name, 类<?>... parameterTypes);

类名

String getName();

Field成员变量¶

设置值

void set(Object obj, Object value);

获取值

get(Object obj);

忽略访问权限

setAccessible(true);

举例¶

public class TestCheck {
    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        Class class = calculator.getClass();
        Method[] methods = class.getMethods();

        int errNum = 0;
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("bug.txt"));

        for (Method method : methods) {
            if (method.isAnnotationPresent(Check.class)) {
                try {
                    method.invoke(calculator);
                } catch (Exception e) {
                    errNum++;
                    bufferedWriter.write(method.getName() + " 方法出现异常了");
                    bufferedWriter.newLine();
                    bufferedWriter.write("异常的名称：" + e.getCause().getClass().getSimpleName());
                    bufferedWriter.newLine();
                    bufferedWriter.write("异常的原因：" + e.getCause().getMessage());
                    bufferedWriter.newLine();
                    bufferedWriter.write("-----------");
                }
            }
        }

        bufferedWriter.write("本次测试一共出现" + errNum + "次异常");
        bufferedWriter.flush();
        bufferedWriter.close();
    }
}

public class Calculator {
    @Check
    public void add() {
        System.out.println("1 + 0 = " + ( 1 + 0));
    }

    @Check
    public void sub() {
        System.out.println("1 - 0 = " + (1 - 0));
    }

    @Check
    public void mul() {
        System.out.println("1 * 0 = " + (1 * 0));
    }

    @Check
    public void div() {
        System.out.println("1 / 0 = " + (1 / 0));
    }

    public void show() {
        System.out.println("此方法不被测试");
    }
}