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Trail: Learning the Java Language
Lesson: Numbers and Strings
Home Page > Learning the Java Language > Numbers and Strings
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# Answers to Questions and Exercises: Numbers

## Questions

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?

       Integer.valueOf(1).equals(Long.valueOf(1))

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

## Exercises

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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