pitfall when implementing multiple interfaces

最新推荐文章于 2019-03-22 11:09:35 发布

原创最新推荐文章于 2019-03-22 11:09:35 发布 · 119 阅读

0 ·

CC 4.0 BY-SA版权

Thinking in Java 专栏收录该内容

155 篇文章

订阅专栏

本文探讨了在Java中实现多个接口时可能出现的方法签名和返回类型冲突问题。通过具体代码示例，详细解释了如何解决这些冲突，并提供了有效的解决方案。强调了在设计接口时应避免使用相同方法名以提高代码的可读性和维护性。

An identical method is not a problem in multiple interfaces, but what if the method differs by signature or return type? Here’s an example:

// interfaces/InterfaceCollision.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.

interface I1 {
  void f();
}

interface I2 {
  int f(int i);
}

interface I3 {
  int f();
}

class C {
  public int f() {
    return 1;
  }
}

class C2 implements I1, I2 {
  @Override
  public void f() {}

  @Override
  public int f(int i) {
    return 1;
  } // overloaded
}

class C3 extends C implements I2 {
  @Override
  public int f(int i) {
    return 1;
  } // overloaded
}

class C4 extends C implements I3 {
  // Identical, no problem:
  @Override
  public int f() {
    return 1;
  }
}

// Methods differ only by return type:
// - class C5 extends C implements I1 {} // [1]
// - interface I4 extends I1, I3 {} // [2]

After uncomment [1] and [2], we use

$ javac interfaces/InterfaceCollision

the compile error is:

javac: invalid flag: interfaces/InterfaceCollision
Usage: javac <options> <source files>
use -help for a list of possible options

when we use

$ javac interfaces.InterfaceCollision

the compile error is:

error: Class names, 'interfaces.InterfaceCollision', are only accepted if annotation processing is explicitly requested
1 error

The solution is to use

$ javac interfaces/InterfaceCollision.java

My error message is:

interfaces/InterfaceCollision.java:50: error: C5 is not abstract and does not override abstract method f() in I1
class C5 extends C implements I1 {}
^
interfaces/InterfaceCollision.java:52: error: types I3 and I1 are incompatible; both define f(), but with unrelated return
types
interface I4 extends I1, I3 {}
^
2 errors

Using the same method names in different interfaces when you expect those interface to be combined generally causes confusion in the readability of the code. Strive to avoid it.

references:

1. On Java 8 - Bruce Eckel

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

3. https://stackoverflow.com/questions/5063266/javac-error-class-names-are-only-accepted-if-annotation-processing-is-explicitl