string split()

 String[] xwb_ids = "".split(":");
   System.out.println(xwb_ids.length);

1

split后长度最小是1

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 String[] xwb_ids = "abc".split(":");
   System.out.println(xwb_ids.length);

1

***********************************

 String[] xwb_ids = "abc:".split(":");
   System.out.println(xwb_ids.length);

1

***********************************

 String[] xwb_ids = "abc:  ".split(":");
   System.out.println(xwb_ids.length);

2

**********************************

 String[] xwb_ids = "abc:bcd".split(":");
   System.out.println(xwb_ids.length);

2