class reverse_String{
    public static void main (String[] args){
        String s1 = "      java php .net    ";
        String s2 = reverseString(s1);
        System.out.println(s2);
    }
    public static void reverseString(String str, int start, int end){
        char[] chs = str.toCharArray();//字符串變數組

        reverseArray(chs,start,end);//反轉數組

        retrun new String(chs);//將數組變字符串
    }
    public static void reverseString(String str){
        retrun reverseString(str,0,str.length());
    }

    public static void reverseArray(char[] arr,int x , int y){
        for(int start = x,end=y-1; start<end; start++,end--){
           swap(arr,start,end);
        }
    }
    private static void swap(char[] arr,int x ,int y){
        char temp = arr[x];
        arr[x] = arr[y];
        arr[y] = temp;
    }

}