为什么会投INT []反对意见,但不反对[]? [英] Why can you cast int[] to Object, but not to Object[]?
问题描述
所以这个作品:
INT I;
对象=(对象)我;
INT []吨;
对象B =(对象)吨;
的String [] S;
[对象] T =(对象[])S;
但是,这并不:
INT []吨;
[对象] Z =(对象[])吨;
所有的一切我得到的第一部分(拳击),但我觉得它非常直观第二部分不起作用。是否有一个具体原因(旁边字符串从Object继承和Int不能从Object继承)?
编辑:
要改进我的问题,这也可以工作:
int类型的= 2;
INT B = 3;
INT C = 4;
INT D = 2;
[对象] 0 =新的对象[] {A,B,C,D};
但随后下列不:
INT [] T =(INT [])O;
令人惊讶你的字符串得到同样的问题:
字符串SA =A;
串SB =B;
字符串SC =C;
串SD =D;
[对象]所以=新对象[] {SA,SB,SC,SD};
的String [] ST =(字符串[])左右;
收益率的最后一行类转换异常。还是这个作品:
对象[] = SY(对象[])新的String [] {SA,SB,SC,SD};
的String [] = SZ(字符串[])SY;
我刚刚发现我一直在寻找自己的答案。你之所以不能施放 INT []
到对象[]
不是因为int是一种原始的,不延长对象
,但因为 INT []
本身并没有延长对象[]
。在code:
INT [] T = INT新[0];
对象OT = T;
的System.out.println(OT的instanceof对象[]);
// - >版画假
的String [] S =新的String [0];
对象OS =秒;
的System.out.println(OS INSTANCEOF对象[]);
// - >版画真
编辑:拳击是必要的,因为Eclipse的人都知道 INT []
和对象[]
是不兼容的
编辑二:顺便说一下这个如果(OBJ的instanceof对象[])
允许请检查是否盒装阵列是一种原始类型的数组
So this works:
int i;
Object a = (Object) i;
int[] t;
Object b = (Object) t;
String[] s;
Object[] t = (Object[]) s;
But this does not:
int[] t;
Object[] z = (Object[]) t;
All in all I get the first part (boxing), but I find it highly unintuitive that the second part does not work. Is there a specific reason why (beside String inheriting from Object and int not inheriting from Object)?
Edit:
To refine my question, this also works:
int a = 2;
int b = 3;
int c = 4;
int d = 2;
Object[] o = new Object[] {a,b,c,d};
But then the following does not:
int[] t = (int[]) o;
Surprisingly you get the same problem with String:
String sa = "a";
String sb = "b";
String sc = "c";
String sd = "d";
Object[] so = new Object[] {sa,sb,sc,sd};
String[] st = (String[]) so;
Yields a class cast exception on the last line. Still this works:
Object[] sy = (Object[])new String[]{sa,sb,sc,sd};
String[] sz = (String[]) sy;
I just found the answer I was looking for myself. The reason why you cannot cast int[]
to Object[]
is not because int is a primitive and does not extend Object
, but because int[]
itself does not extend Object[]
. In code:
int[] t = new int[0];
Object ot = t;
System.out.println(ot instanceof Object[]);
// --> prints 'false'
String[] s = new String[0];
Object os = s;
System.out.println(os instanceof Object[]);
// --> prints 'true'
Edit: the boxing is necessary because Eclipse knows that int[]
and Object[]
are incompatible.
Edit II: Btw this if(obj instanceof Object[])
allows to check wether a boxed array is an array of a primitive type.
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