数组下标检查的坑？

int[] a = new int[]{25,6,56,17,8};

for (int i=1; i<5; i++) {

int temp = a[i];

int xia = i-1;

while( xia>=0 && temp<a[xia] )  //这个能正常运行，对的

//while( temp<a[xia] && xia>=0 )  //这个会报错。。。Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 真令人摸不着头脑

{

a[xia+1] = a[xia];

xia--;

}

a[xia+1] = temp;

}