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Trail: Learning the Java Language
Lesson: Object Basics and Simple Data Objects

## Questions and Exercises: Numbers

### Questions

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

> > a. 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"?

> > b. What two `Integer` methods 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.

> > c. 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?

> >     new Integer(1).equals(new Long(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.java`.

> 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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