int數(shù)組和string數(shù)組

int [] a1 = new int[]{1,2,3};
int [] a2 = new int[4];
int[][] a3 = new int[2][3];
String [] a4 = new String[]{"a","b","c"}; 
                    
Object aObj1 = a1;   //正確，因?yàn)镮nt數(shù)組是Object
Object aObj2 = a4;
//Object[] aObj3 = a1; 錯(cuò)誤，因?yàn)榛绢愋虸nt不是Object
Object[] aObj4 = a3;  //正確，因?yàn)镮nt數(shù)組是Object
Object[] aObj5 = a4;

為什么a4既可以賦值給object，有可以賦值給object數(shù)組，但是int就不行