判定给定数组是否已经排好序

public class Test{
    public static boolean isOrdered(Comparable a[]){
        int j=0, n = a.length;
        while(j<n-1 && a[j].compareTo(a[j+1])==0) j++;
        if(n<=1 || j==n-1)
            return true;
        else
            j = a[j].compareTo(a[j+1]);
        for(int i=0; i<n-1; i++)
            if(a[i].compareTo(a[i+1])*j < 0)
                return false;
        return true;
    }
    public static void main(String[] args){
        Integer arr[] = {1,2,3,4,5};
        Integer arr1[] = {5,4,3,2,1};
        Integer arr2[] = {1,2,5,4,3};

        System.out.println(isOrdered(arr)); //true

        System.out.println(isOrdered(arr1));//true

        System.out.println(isOrdered(arr2));//false


    }
}