java - 为什么 Java 中字符串比较结果不打印 0,1 或 -1？

Question

我必须比较一个日期并检查它是否在一个范围内。我输入了两个日期，一个是开始日期，另一个是结束日期。比较日期不应早于开始日期或晚于结束日期。

我将它们全部作为字符串并将它们全部分割。

当我将日期与开始日期进行比较时，这是可以的。但与完成日期月份相比，它显示的结果是6。它应该显示 1、0 或 -1 的结果，因为我正在比较字符串。

以下是来源，我已在遇到问题的行上方进行了评论。还给出了示例输入和输出。我哪里出错了？

System.out.println("................");

//store the value of start date limit.
String[] startDate  =   start_jTextField1.getText().split("-");

//store the value of start date limit.
String[] finishDate =   finish_jTextField2.getText().split("-");

//store the date that have to check.
String[] check_this_date = Check_this_Date_jTextField1.getText().split("-");

System.out.println("start:");
for(String start : startDate )
{
    System.out.println(start);
}

System.out.println("Finish:");
for(String finish : finishDate )
{
    System.out.println(finish);
}

System.out.println("Check:");
for(String checkDate : check_this_date )
{
    System.out.println(checkDate);
}


boolean start_range_check   = false;
boolean finish_range_check  = false;

//My question is about the next line and why it is printing 6.
//It should print 0, 1, or -1.
System.out.println("Before Finish check block(month):\n"+ check_this_date[1].compareTo( finishDate[1] ) );

System.out.println("Before Finish check block(day compare):\n"+ check_this_date[0].compareTo( finishDate[0] ) );//here date will be compared with finish date's date.

if( check_this_date[2].compareTo(startDate[2]) == 1 ||  check_this_date[2].compareTo(startDate[2]) == 0)//if year greater or equal to from start range year.
{
    System.out.println("starZone:"+start_range_check);//print the current start_range_check  value to ensure that above condition has satisfied.
    if(check_this_date[1].compareTo(startDate[1]) == 1 ||  check_this_date[1].compareTo(startDate[1]) == 0)//if month greater or equal to from start range month.
    {
        System.out.println("starZone:"+start_range_check);//print the current start_range_check  value to ensure that above condition has satisfied.
        if(check_this_date[0].compareTo(startDate[0]) == 1 ||  check_this_date[0].compareTo(startDate[0]) == 0)//if day greater or equal to from start range day.
        {
            start_range_check = true;
            System.out.println("starZone:"+start_range_check);//print the current start_range_check  value to ensure that above condition has satisfied and start_range_check changed.
        }
    }
}

if(check_this_date[2].compareTo( finishDate[2] ) == -1 || check_this_date[2].compareTo( finishDate[2] ) == 0 )
{
    System.out.println("finishZone result(year):\n"+check_this_date[2].compareTo( finishDate[2]) );//print the comparision result.

    System.out.println("finishZone(before month checking):\n"+check_this_date[1].compareTo( finishDate[1]) );//print the comparision result.my question why the result is 6 here.

    if(check_this_date[1].compareTo( finishDate[1] ) == -1 || check_this_date[1].compareTo( finishDate[1] ) == 0 )
    {
        System.out.println("finishZone"+start_range_check);
        if(check_this_date[0].compareTo( finishDate[0] ) == -1 || check_this_date[0].compareTo( finishDate[0] ) == 0 )
        {
            finish_range_check = true;
            System.out.println("finishZone"+start_range_check);//print the current start_range_check  value to ensure that above condition has satisfied and start_range_check changed.
        }
    }
}

if( finish_range_check == true && start_range_check == true )
{
    result_jLabel2.setText("Within Range.");
}
else
{
    result_jLabel2.setText("Not in Range");
}


Sample input and output:
Date Format: dd-MM-yyyy
................
start:
28
6
2015
Finish:
28
12
2015
Check:
28
7
2015
Before Finish check block(month comparing):
6
Before Finish check block(day comparing):
0
starZone:false
starZone:false
starZone:true
finishZone result(year):
0
finishZone(before month checking):
6

Answer 1

阅读 compareTo() 的javadoc :

Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

它没有指定负数或正数的实际值，因此您不能期望它是 -1或1 .

当使用compareTo()时您应该始终检查结果为 < 0 , <= 0 , == 0 , >= 0 , > 0 ，或!= 0 ，取决于您的需要。
基本上date1.compareTo(date2) <= 0 Java 语言中的 date1 <= date2 .