Several ways to remove spaces from Java strings

1. remove leading and trailing spaces

   String str = "Hello java!  ";
   System.out.println(str.trim());
   

2. Remove all spaces, including the middle

   String str = "Hello java!  ";
   
   String str2 = str.replaceAll(" ", "");
   System.out.println(str2);
   

3. Replace most whitespace characters, not limited to spaces

   String str = "Hello java!  ";
   
   String str3 = str.replaceAll("\\s*","");
   System.out.println(str3);
   

   Among them, \s can match blank characters such as spaces, tabs, and form
   feeds Java regular expressions