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;
 

解决方案

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[]）;
//  - ＆GT;版画假
的String [] S =新的String [0];
对象OS =秒;
的System.out.println（OS INSTANCEOF对象[]）;
//  - ＆GT;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;

解决方案

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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