[英]What kind of Exception occurred?
I tried to create a test ClassCastException: 我试图创建一个测试ClassCastException:
In line 1: it prints out class cast exception
as I expected 在第1行:它按照我的预期打印出class cast exception
In line 2: it just prints exception.RuntimeExceptionTest$1B@7852e922
(RuntimeExceptionTest is my class name). 在第2行:它只打印exception.RuntimeExceptionTest$1B@7852e922
$ 1B@7852e922(RuntimeExceptionTest是我的类名)。 I wonder what kind of exception here? 我想知道这里有什么样的例外?
try {
class A { }
class B extends A {}
class C extends A {}
A objA = new B();
System.out.println((C)objA); // Line 1
System.out.println((A)objA); // Line 2
} catch (Exception e) {
e.printStackTrace();
}
Line2 doesn't throw an exception. Line2不会抛出异常。 From the Oracle javadocs: 来自Oracle javadocs:
The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. 类Object的toString方法返回一个字符串,该字符串由对象为实例的类的名称,符号字符“@”和对象的哈希码的无符号十六进制表示组成。 In other words, this method returns a string equal to the value of: 换句话说,此方法返回一个等于值的字符串:
getClass().getName() + '@' + Integer.toHexString(hashCode())
That means your Line2 just prints what objA.toString() returns, which is 这意味着你的Line2只打印objA.toString()返回的内容,即
exception.RuntimeExceptionTest$1B@7852e922
since exception.RuntimeExceptionTest is your class name. 因为exception.RuntimeExceptionTest是你的类名。
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