stanford編程方法——習題答案(the art and science of java)——chapter05

 

Chapter 05 Methods
Review questions

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1. Explain in your own words the difference between a method and a program.

Answer:
    lies in who or what makes use of it

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2. Define the following terms as they apply to methods: call, argument,
return.
Answer:
    call: to apply a mehtod
    aruments: pass the
paramter to a method
    return: return a result from a method   

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3. What is the difference between passing information to a method by using

arguments and reading input data using methods like readInt? When would each

action be appropriate?
Answer:
    Input and output refer to
communication between a program and its user.
Arguments and results
represetn communication between a method and its caller.

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4. How do you specify the result of a method in Java?
Answer:
   
return expression;

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5. Can there be more than one return statement in the body of a method?

Answer:
    yes. for example:
    private double min(double x,
double y)
    {
        if (x < y)
            return x;

        else
            return y;
    }

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6. How do you indicate that you want to apply a method to another object?

Answer:
    reciever.name(arguments);

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7. Why has it been unnecessary to specify receivers in the programs
presented in
the earlier chapters?
Answer:
    for those methods
have defined in their superclass   

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8. Why was it unnecessary to include a break statement at the end of each
case
clause in the monthName method presented in the chapter?
Answer:

    return statements automatically exit from the entire method

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9. What is a predicate method?
Answer:
    return values of type
boolean

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10. How do you tell whether two strings contain the same characters?

Answer:
    private boolean haveSameCharacter(String s1, String s2)

    {
        for (int i = 0; i < s1.length(); i++)
           
for (int j=0; j<s2.length(); j++)
                if (s1[i] == s2[j])

                    return true;

        return false;
    }

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11. What is the relationship between arguments and formal parameters?

Answer:
    copy

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12. Variables declared within a method are said to be local variables. What
is
the significance of the word local in this context?
Answer:
   
the variable scope

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13. What does the term return address mean?
Answer:
    the point at
which execution should continue

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14. What is a brute-force algorithm?
Answer:
    int gcd(int x, int
y)
    {
        int guess = Math.min(x, y);
        while (x %
guess != 0 || y % guess != 0)
            guess--;
        return guess;

    }   

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15. Use Euclid’s algorithm to compute the greatest common divisor of 7735
and
4185.  What values does the local variable r take on during the
calculation?
Answer:
    3350
    835               
    10

    5
    0

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16. In the examples of Euclid’s algorithm to calculate gcd(x, y) that appear
in
this chapter, x is always larger than y. Does this condition matter? What

happens if x is smaller than y?
Answer:
    doesn't matter
   
if x < y, then r = x % y = x and x != 0, so x = y and y = r
    then y
> x;

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Programming exercises

1. Write a program that displays the value of the mathematical constant

This constant φ is called the golden ratio. Classical mathematicians believed that this
number represented the most aesthetically pleasing ratio for the dimensions of a
rectangle, but it also turns up in computational mathematics.

 

 

/*<br /> * File: GoldenRatio.java<br /> * -----------------------<br /> * This program dispalys the golden ratio.<br /> * fi = (1 + sqrt(5)) / 2;<br /> */<br />import acm.program.*;<br />import java.lang.Math;<br />public class GoldenRatio extends ConsoleProgram {<br />public void run() {<br />double fi = (1 + Math.sqrt(5)) / 2;<br />println("golden ratio: fi = " + fi);<br />}<br />}<br />