Problem Set To ensure that you understand all the material in this lecture, please solve the the announced problems after you read the lecture.
If you get stumped on any problem, go back and read the relevant part of the lecture. If you still have questions, please get help from the Instructor, a CA, or any other student.
- Write a statement that calls any of the "result-returning" methods [maybe just display the returned result on the console] and hand simulate its execution with a call frame.
- Java allows methods to have no parameters; such methods are defined and called by specifying their name followed and an empty argument list: e.g., f[]. Use your knowledge of the semantics of the return statement to explain what happens for the following method and its calls. Don't get confused by what you think it does [or want it to do]: follow the rules. int f[] { return 1; return 2; } What is displayed by System.out.print["1st f = " + f[] + " 2nd f = " + f[]];
- Write
a method named characteristic, which returns 1 if its parameter is true and 0 if its parameter is false.
- Write a method named abs, which returns the absolute value of its int parameter [it always returns the non-negative magnitude of its parameter; don't call the Math.abs method].
- Write a method named signum, which returns -1 if its double parameter is negative, 0 if its parameter is zero, and +1 if its parameter is positive.
- Write a method named constrain. Calling constrain[1,5,10] returns 5 because this middle value is between the first and third values. Calling constrain[1,-5,10] returns 1 because this middle value is smaller than the first value, so the method returns the first value. Calling constrain[1,15,10] returns 10 because this middle value is larger than the third value, so the method returns the third value. Thus, this method returns the middle value, but it is constrained to lie between the first and third values inclusize.
- Write a method named forChar. We could call the method as forChar["Enter an Upper-Case Letter", 'A', 'Z'] which always returns a char whose ASCII value is between 'A' and 'Z'; or we could call the method as forChar["Enter a Digit", '0', '9'] which always returns a char whose ASCII value is between '0' and '9'.
- Why can't we write a simple method named makeChange, which is supplied the amount of change to vend, and returns the number of quarters, dimes, nickels, and pennies needed to vend the required change. How do you think we can write a method to solve such a problem?
- Write a method named majority, which returns the most frequently occuring value of its three boolean parameters: no matter the values, at two of three [and possibly three of three] will have the same value. For example, the call majority[true,false,false] returns false, while the call majority[true,true,true] returns true.
- Write a method named median, which returns the middle value of its three arguments. For example, the call median[3,2,5] returns 3 because it is between 2 and 5.
- Assume that we declare char roman; and store in it a character that is a roman numeral. Write a method that returns the int equivalent
of the Roman numeral: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, M is 1000; if it stores any other character, return -1.
- Write a method named isPrime, which returns whether or not its parameter is a prime number. A prime number has only 1 and itself as divisors: neither 0 nor 1 are considered prime; 2 is the smallest prime number, then 3, 5, 7, 11, etc. Hint: Use a for loop to check for possible divisors, along with the % operator.
- Write a method named harmonic, which takes one int parameter and returns a double value representing the harmonic series of that order. harmonic[n] is defined as 1 + 1/2 + 1/3 + ... 1/n. So harmonic[2] returns 1.5; and harmonic[4] returns 2.083333.
- Write a method named fw, which returns the number of characters needed to print its integer parameter. For example, fw[5] returns 1; fw[-5] returns 2; fw[453] returns 3; and fw[-243] returns 4. Hint: the number of digits in a number is related to how many times you can divide it by 10 and still have a non-zero value; treat negative numbers specially.
- Write a method named block that has an int height and width parameter, and a char parameter. This method returns a String which when printed displays a rectangle of that the specified height and width, consisting of the specified character. Calling System.out.println[block[5,20,'*']]; would print. ******************** ******************** ******************** ******************** ******************** Remember that catenating an escape sequence character ['\n'] in a String causes a carriage return when that character is printed.
- Suppose our program consists of the the methods main, a, b, c, d, and e. Also suppose main calls a,
b, d, and e, a calls c, b calls a, c calls nothing else, d calls a, and e calls d and c.
- Find two "natural orders" in which to write these methods in a file
- Find two "reverse natural orders" in which to write these methods in a file
- For all the sample methods in this lecture, identify the ones in which it makes sense to throw IllegalArgumentExceptions and describe under what conditions. Note that sometimes individual parameters will store reasonable values, but pairs of parameters will have values that are incompatible.
- As we saw in this lecture, we can specify that a parameter variable is final. For example, we can rewrite factorial as public static int factorial [final int n]
{
int answer = 1;
for [int i=2; i