java – Boxing to Object类型以避免编译失败

参见英文答案 > Why doesn’t autoboxing overrule varargs when using method overloading in Java 7?                                    3个
请考虑以下代码

public class Foo
{

  int value;
  public Foo (final String str, Object ... bug)
  {
    System.out.println ("Should work! 1");
  }

  public Foo (final String str, final int value, Object ... bug)
  {
     this.value = value;
    System.out.println ("Should work! 2");
  }

  public static void main (String[]args)
  {
    Foo f = new Foo ("Foo", 3); //Line 14
    System.out.println(f.value);
  }
}

当我使用jdk-1.6.x时,我成功地编译了它.
但升级到jdk-1.7后,它给了我错误：

Foo.java:18：错误：对Foo的引用是不明确的,Foo中的构造函数Foo(String,Object …)和Foo中的构造函数Foo(String,int,Object …)匹配
    Foo f = new Foo(“Foo”,3); //第14行

所以为了避免这个错误,我改变了第二个Ctor

  public Foo (final String str, final Integer value, Object ... bug)
  {
     this.value = value;
    System.out.println ("Should work! 2");
  }

这样它就可以自动装箱到Integer并跳过编译错误.

几个问题：
1)这是一个好习惯吗？如果没有那么还有其他方法吗？
2)为什么java开发人员会决定提供错误而不是允许它？

解决方法:

这是设计和Java 6和Java 7之间不兼容的已知区域,因为过载分辨率算法在Java 7中已得到修复.在Java 5和6中,以下代码无法编译：

class Test {
    void foo(int... i) {}
    void foo(double... d) {}

    void test() {
       foo(1,2,3);
    }
}

编译器会抱怨调用不明确.但这不是真的,因为double比int更通用,因此在这种情况下int是最具体的选项.

但是,此修复导致不兼容(请查看release notes;搜索“varargs”).结果是当你有int和Object时你不能选择最具体的方法,因为它们都不是另一个的子类型.所以这不应该编译.但是,您可以使用Integer,因为Integer是Object的子类型,在这种情况下,它是最具体的选项,因此编译器可以选择它.

发行说明中的​​相关部分：

While the javac compiler accepts more code than it did prior to JDK 7, this fix also results in a slight source incompatibility in the following case:

class Test {
    void foo(int... i) {}
    void foo(Object... o) {}

    void test() {
       foo(1,2,3);
    }
}

This code compiles in JDK 6 (the most specific method is foo(int...)). This code does not compile under JDK 7. As per 07001, it is not possible to choose between foo(int...) and foo(Object...) as neither int is a subtype of Object, nor Object is a subtype of int. This program should be disallowed (in fact, it should never have been allowed in the first place).

Nature of Incompatibility: behavioral and source

RFE: 07002

标签：java,java-7,autoboxing
来源： https://codeday.me/bug/20190901/1780418.html