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The Java™ Tutorials
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Numbers and Strings
Numbers
The Numbers Classes
Formatting Numeric Print Output
Beyond Basic Arithmetic
Summary of Numbers
Questions and Exercises
Characters
Strings
Converting Between Numbers and Strings
Manipulating Characters in a String
Comparing Strings and Portions of Strings
The StringBuilder Class
Summary of Characters and Strings
Autoboxing and Unboxing
Questions and Exercises
Trail: Learning the Java Language
Lesson: Numbers and Strings
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# Questions and Exercises: Numbers

## Questions

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

   1. 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"?

   2. 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.

   3. What Double method can you use to detect whether a floating-point number has the special value Not a Number (`NaN`)?

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

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

## Exercises

1. 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?

2. 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`.

3. 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 (`.`).

Check your answers.

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