1.14 标准注解

1.14.1 The Built-In Annotations 内建注解

Java defines seven built-in annotations.

Four are imported from java.lang.annotation: @Retention, @Documented, @Target, and @Inherited.

 

Three, @Override, @Deprecated, and @SuppressWarnings, are included in java.lang.

Java定义了 7 种内建注解:

其中 4 种从 java.lang.annotation导入:

@Retention

@Documented

@Target

@Inherited

另外3中包含在java.lang中:

@Override

@Deprecated

@SuppressWarnings

 

1.14.2 Standard Annotations: Override

Override is a marker annotation type that can be applied to a method to indicate to the compiler that the method overrides a method in a superclass. This annotation type guards the programmer against making a mistake when overriding a method. For example, consider this class Parent:

@Override 是标记型注解, 可以应用于方法, 指示编译器该方法覆盖父类的一个方法.

此注解防止编程者在覆盖一个方法时犯错. 例如: 下面的代码编译不通过, 因为父类中没有相同的方法签名.

class Parent {
    public float calculate (float a, float b) {
        return a * b;
    }
}
//Whenever you want to override a method, declare the Override annotation type before the method:

public class Child extends Parent {
    @Override
    public int calculate (int a, int b) {
        return (a + 1) * b;
    }
}

 1.14.3 Standard Annotations: Deprecated 不推荐, 藐视

Deprecated is a marker annotation type that can be applied to a method or a type (class/interface) to indicate that the method or type is deprecated.

@Deprecated 是 标记型注解, 可用于方法或类/接口, 指示该方法或类型不被推荐.

If you use or override a deprecated method, you will get a warning at compile time.

如果你使用或覆盖一个不推荐的方法, 在编译时会收到一个警告.

public class DeprecatedTest2 {
  public static void main(String[] args) {
    DeprecatedTest test = new DeprecatedTest();
    test.serve();
  }
}

class DeprecatedTest {
  @Deprecated
  public void serve() {

  }

}