Answers to Questions and Exercises: Numbers - Java Tutorial 5.0 英文版

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Answers to Questions and Exercises: Numbers

Questions

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

Question 1a: 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 1a: toHexString

Question 1b: 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.
Answer 1b: valueOf and intValue. Here's how:

	String base5String = "230";
        int result = Integer.valueOf(base5String, 5).intValue();

Question 1c: What Double method can you use to detect whether a floating-point number has the special value Not a Number (NaN)?
Answer 1c: isNaN

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

new Integer(1).equals(new Long(1))

Answer 2: False. The two objects (the Integer and the Long) have different types.

Exercises

Exercise 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?
Answer 1: 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

Exercise 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.
Answer 2: See Adder.

Exercise 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 (.).
Answer 3: See FPAdder.

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