Java 中的 ClassCastException
我在下面的代码中遇到了 ClassCastException，这对我来说没有多大意义，因为 targetObject 是一个 Comparable，而 current 是一个 ToBeFound。整数和字符串从哪里来？
ToBeFound origin = new ToBeFound();
public ToBeFound findWrapper(Comparable targetObject)
{
return find(origin, targetObject);
}
private ToBeFound find(ToBeFound current, Comparable targetObject)
{
if (current == null)
{
return null;
}
System.out.println(targetObject.compareTo(current.getValue()));
// Exception in thread "main" java.lang.ClassCastException:
// java.lang.Integer cannot be cast to java.lang.String
return new ToBeFound();
}
//body of main() that calls the methods
master.find( (Comparable) scanner.next());
// Scanner is a java.util.Scanner scanning System.in
I'm getting a ClassCastException in the below code, which doesn't make much sense to me, as targetObject is a Comparable and current is a ToBeFound. Where are the Integer and String coming from?
ToBeFound origin = new ToBeFound();
public ToBeFound findWrapper(Comparable targetObject)
{
return find(origin, targetObject);
}
private ToBeFound find(ToBeFound current, Comparable targetObject)
{
if (current == null)
{
return null;
}
System.out.println(targetObject.compareTo(current.getValue()));
// Exception in thread "main" java.lang.ClassCastException:
// java.lang.Integer cannot be cast to java.lang.String
return new ToBeFound();
}
//body of main() that calls the methods
master.find( (Comparable) scanner.next());
// Scanner is a java.util.Scanner scanning System.in
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评论（4）
正如
compareTojavadoc 所述：看来您的
target是String类型，即Comparable和current.getValue()返回Integer类型的对象。您可以尝试执行
String.valueOf(current.getValue)如果它工作正常那么我是对的。 :)As
compareTojavadoc states:It seems that your
targetis of aStringtype which isComparable<String>andcurrent.getValue()returns an object ofIntegertype.You can try to do
String.valueOf(current.getValue)if it works ok then I'm right. :)看起来
current是一个TreeNode...Looks like
currentis aTreeNode...将原始 int 转换为 String
compareTo的返回类型是 int，因此您可以使用What is the type of target? ？看起来您正在将字符串与整数进行比较。Return type of
compareTois int, so you can convert your primitive int to String usingWhat is the type of target? Seems like you are comparing String against Integer.
如果您的示例代码反映了您实际运行的内容，则：
您的代码未显示
target的声明，但异常消息暗示它必须是<代码>字符串。 （您显示使用targetObject的声明...但这不是代码实际使用的！！）您的代码没有显示
ToBeFound.getValue( )方法...但异常消息暗示它必须是Integer。如果参数对象不是字符串，
String.compareTo(Object)会抛出 CCE。If your sample code is reflects what you are actually running then:
Your code does not show the declaration for
target, but the exception message implies that it must beString. (You show use the declaration fortargetObject... but that's not what the code is actually using!!)Your code doesn't show the declaration for the
ToBeFound.getValue()method ... but the exception message implies that it must beInteger.The
String.compareTo(Object)throws a CCE if the parameter object is not a String.