Question

假设我有一个名为foo的方法，将2个Object作为参数。两个对象属于同一类型，并且都实现了可比较的接口。

void foo(Object first, Object second){

    if (!first.getClass().isInstance(second))   //first and second of the same type
        return;

    Comparable firstComparable = (Comparable)first;  //WARNING
    Comparable secondComparable = (Comparable)second;  //WARNING

    int diff = firstComparable.compareTo(secondComparable);  //WARNING
}

前两个警告是：

可比较是原始类型。对泛型类型的引用可比较应该参数化

最后警告：

类型安全：方法compareTo（Object）属于原始类型可比。对泛型类型的引用应该是参数

如何重构我的代码以删除这些警告？

编辑：我可以不改变foo方法的签名吗？

Answer 1

你必须告诉编译器它们是相同的类型和可比较的。如果您无法更改签名，则可以添加一种向后兼容的方法。

@SuppressWarnings("unchecked")
static void foo(Object first, Object second) {
    foo((Comparable) first, (Comparable) second);
}

static <T extends Comparable<T>> void foo(T first, T second){
    int diff = first.compareTo(second); // no warning.
}

Answer 2

无需更改签名即可

    void foo(Object first, Object second){

        if (!first.getClass().isInstance(second)) 
            return;

        Comparable<Object> firstComparable = (Comparable<Object>)first;  
        Comparable<Object> secondComparable = (Comparable<Object>)second; 

        int diff = firstComparable.compareTo(secondComparable);  
    }

但是你还有：
Type safety: Unchecked cast from Object to Comparable<Object>

但没有Comparable is a raw type. References to generic type Comparable<T> should be parameterized
并且没有Type safety: The method compareTo(Object) belongs to the raw type Comparable. References to generic type Comparable<T> should be parameterized

Answer 3

你必须使用 Comparable<Type>其中Type是实现Comparable的对象。

首先，为什么你的方法参数实例为Objects？如果您确定参数类型相同，则应使用特定类作为参数。如果可以具有类的层次结构，则在层次结构中使类最高。让Object获得一般功能永远不是一个好主意。

Answer 4

编辑：既然你说你不能改变方法的签名，那么你真的无法逃脱没有不安全（对编译器）演员，以及@SuppressWarnings：

@SuppressWarnings("unchecked")
public void foo(final Object first, final Object second) {
    if (!first.getClass().isInstance(second)) // first and second of the
        return;

    Comparable<Object> firstComparable = (Comparable<Object>) first;
    Comparable<Object> secondComparable = (Comparable<Object>) second;
    int diff = firstComparable.compareTo(secondComparable);
}

Answer 5

添加@SuppressWarnings注释。

@SuppressWarnings("unchecked")
void foo(Object first, Object second){

    if (!first.getClass().isInstance(second))   //first and second of the same type
        return;

    Comparable firstComparable = (Comparable)first;  //WARNING
    Comparable secondComparable = (Comparable)second;  //WARNING

    @SuppressWarnings("unused")
    int diff = firstComparable.compareTo(secondComparable);  //WARNING
}

Java：删除“Comparable是原始类型”警告

5 个答案: