initialize fileds in interfaces

最新推荐文章于 2021-12-08 05:44:36 发布

原创最新推荐文章于 2021-12-08 05:44:36 发布 · 121 阅读

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探讨了在Java接口中使用非常量表达式初始化字段的方法，通过实例展示了如何在接口中定义并初始化Random类型的变量，以及由此产生的各种随机数值。

Fields defined in interfaces cannot be “blank finals,” but they can be initialized with non-constant expressions. For example:

// interfaces/RandVals.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Initializing interface fields with
// non-constant initializers

import java.util.*;

public interface RandVals {
  Random RAND = new Random(47);
  int RANDOM_INT = RAND.nextInt(10);
  long RANDOM_LONG = RAND.nextLong() * 10;
  float RANDOM_FLOAT = RAND.nextLong() * 10;
  double RANDOM_DOUBLE = RAND.nextDouble() * 10;
}

test above code:

// interfaces/TestRandVals.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

public class TestRandVals {
  public static void main(String[] args) {
    System.out.println(RandVals.RANDOM_INT);
    System.out.println(RandVals.RANDOM_LONG);
    System.out.println(RandVals.RANDOM_FLOAT);
    System.out.println(RandVals.RANDOM_DOUBLE);
  }
}
/* Output:
8
-32032247016559954
-8.5939291E18
5.779976127815049
*/

Knowledge:

The fields are not part of the interface. The values are stored in the static storage area for that interface.

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/interfaces/RandVals.java

3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/interfaces/TestRandVals.java