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Thread: Beginner Java Method

  1. #1
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    Default Beginner Java Method

    Beginner warm up problem that I can't figure out why isn't working. Thanks for any assistance in advance. (Note: Trying to use substring method not charAt() method.)

    ----------------------

    Given a string, return a string made of the first 2 chars (if present), however include first char only if it is 'o' and include the second only if it is 'z', so "ozymandias" yields "oz".

    public String startOz(String str) {
     
    String r = ""; 
     
      if (str.substring(0).equals("o")) 
      r = str.substring(0);  
     
      if (str.substring(1).equals("z")) 
      r = str.substring(1); 
     
      return r;
    }

    Expected Run
    startOz("ozymandias") → "oz" "" X
    startOz("bzoo") → "z" "" X
    startOz("oxx") → "o" "" X
    startOz("oz") → "oz" "z" X
    startOz("ounce") → "o" "" X
    startOz("o") → "o" "o" OK
    startOz("abc") → "" "" OK
    startOz("") → "" "Exception:java.lang.StringIndexOutOfBoundsExcepti on: String index out of range: -1 (line number:8)" X
    startOz("zoo") → "" "" OK
    startOz("aztec") → "z" "" X
    startOz("zzzz") → "z" "" X
    startOz("oznic") → "oz" "" X

    CodingBat Java Warmup-1 startOz


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Beginner Java Method

    "Exception:java.lang.StringIndexOutOfBoundsExc epti on: String index out of range: -1
    Code should always test that the data is what is expected. In this case the code expected a String with at least 1 character. The String class's length method would help here.

    If you can not understand what the code is doing, add a println() statement before the if statement that prints out the String returned by the substring method so you can see what the computer sees when it executes the if statement.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Beginner Java Method

    If it possible to not use the length method? I figured I could get it working with the substring method, but I am having problems.

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Beginner Java Method

    If it possible to not use the length method?
    Well written code checks for error conditions and acts to prevent exceptions.
    If your instructor told you not to do that, it is not a good practice to skip tests like that but you might have to follow your instructor's wishes to get the grade.

    Did you miss the second part of my last post?
    If you don't understand my answer, don't ignore it, ask a question.

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