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Trail: Learning the Java Language
Lesson: Numbers and Strings
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Answers to Questions and Exercises: Numbers


  1. Use the API documentation to find the answers to the following questions:

    1. Question: What Integer method can you use to convert an int into a string that expresses the number in hexadecimal? For example, what method converts the integer 65 into the string "41"?

      Answer: toHexString

    2. Question:What Integer method would you use to convert a string expressed in base 5 into the equivalent int? For example, how would you convert the string "230" into the integer value 65? Show the code you would use to accomplish this task.

      Answer: valueOf. Here's how:

      String base5String = "230";
      int result = Integer.valueOf(base5String, 5);
    3. Question: What Double method can you use to detect whether a floating-point number has the special value Not a Number (NaN)?

      Answer: isNaN

  2. Question: What is the value of the following expression, and why?


    Answer: False. The two objects (the Integer and the Long) have different types.


  1. Exercise: Change MaxVariablesDemo to show minimum values instead of maximum values. You can delete all code related to the variables aChar and aBoolean. What is the output?

    Answer: See MinVariablesDemo. Here is the output:

    The smallest byte value is -128
    The smallest short value is -32768
    The smallest integer value is -2147483648
    The smallest long value is -9223372036854775808
    The smallest float value is 1.4E-45
    The smallest double value is 4.9E-324
  2. Exercise: Create a program that reads an unspecified number of integer arguments from the command line and adds them together. For example, suppose that you enter the following:

           java Adder 1 3 2 10

    The program should display 16 and then exit. The program should display an error message if the user enters only one argument. You can base your program on ValueOfDemo.

    Answer: See Adder.

  3. Exercise: Create a program that is similar to the previous one but has the following differences:

    • Instead of reading integer arguments, it reads floating-point arguments.
    • It displays the sum of the arguments, using exactly two digits to the right of the decimal point.

    For example, suppose that you enter the following:

    java FPAdder 1 1e2 3.0 4.754

    The program would display 108.75. Depending on your locale, the decimal point might be a comma (,) instead of a period (.).

    Answer: See FPAdder.

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