Revision as of 12:05, 1 December 2011

COMP 1010 Home > User-Defined Methods

Review Questions

Question 1

Explain the relationship between an argument and its corresponding parameter. Do not define argument or parameter.

Question 2

Which of the following methods completes execution first? What does this tell you about the order in which nested methods are executed?

System.out.println( JOptionPane.showInputDialog("Please enter a message:") );

Question 3

What are the valid names that a method name can have?

Question 4

How many parameters can a method have?

Question 5

What is a local variable, and how does it relate to method scope?

Question 6

If the main method and a user-defined method have an int by the same name, how does the program know the difference between them?

Question 7

What is the purpose of the main method in a Java program?

Exercises

Exercise 1

Write a user-defined method which has an int parameter called numReps and returns a String. The String will contain a sequence.

• If numReps is odd, the sequence is "+*".
• If numReps is even, the sequence is "/_".

The parameter numReps determines how many times the sequence is repeated in the String. For example:

• When numReps is 2, the pattern is "/_/_".
• When numReps is 5, the pattern is "+*+*+*+*+*".

When you are finished, write a main method which tests your new user-defined method. Try the inputs 3, 4, and 0.

Exercise 2

Write a user-defined method which calculates the area of a triangle, called getTriangleArea. The formula is:

       base x height
area = _____________

            2

All values are of the double type.

Next, write a method called printArea which accepts a base parameter and a height parameter. The method prints the base, height, and area. Within this method you will call getTriangleArea.

Finally, write a main method which tests printArea. Try the following inputs: base = 2, height = 4; base = 5, height = 3; base = 0, height = 17.

Exercise 3

Identify and correct the problems found in this method:

public static void FindBiggest( num1, num2, num3 )
    if (( num1 > num2 ) && ( num1 > num3 ))
    {
        return num1;
    }
    else if (( num2 > num1 ) && ( num2 > num3 ))
    {
        return num2;
    }
    else
    {
        return num3;
    }

Exercise 4

Write a method called processNumbers which does the following:

1. Takes two doubles, dbl1 and dbl2, as its parameters.
2. Calculate the sum of the two doubles, and store it in a variable called sum.
3. Calls the Math.sqrt function to get the square root of the sum, and return it.

Exercise 5

A palindrome is a string that reads the same, forwards and backwards. Examples of palindromes:

1. STAR RATS
2. WAS IT A RAT I SAW
3. I PREFER PI
4. STAR COMEDY BY DEMOCRATS

Write a method called isPalindrome which does the following:

1. Takes a string as it's only parameter
2. Uses a loop to check is the letters are the same at each ends
3. uses the charAt() function to compare chars.

Exercise 6

Review the code below. What does it print out? Explain your answers.

public class myClass 
{
	public static void main(String[] args)
	{
		int x,y,z;
		
		x = 1;
		y = 2;
		z = 3;
		
		methodTwo();
		
		System.out.println("This is x: " + x);
		
		System.out.println("This is y:" + y);
		
		y = methodOne();
		
		System.out.println("This is y:" + y);
		
		methodTwo();
		
		System.out.println("This is z:" + z);
		
		System.out.println("End of program.");
	}
  
  
	public static int methodOne()
	{
		int x,y,z;
		
		x = 4;
		y = 5;
		z = 6;
		
		return y;
	}
	
	public static void methodTwo()
	{
		int x,y,z;
		
		x = 7;
		y = 8;
		z = 9;
		
	}
 
}

Exercise 7

Write a method which prints the contents of the array on a sigle line and calculates the average of the numbers in the array as given below. The array is as follows: int[] array = {3,12,18,37,169, 55,93,48}

public static void method()
{
	int index, sum = 0, avg;
		
	for(index=0; index < array.length; index++){
              System.out.println(index + ": " + array[index]);
        }//for
		
	for(index=0; index < array.length; index++){
              sum = sum + array[index]);
        }//for 
        
        avg = sum/array.length;
        
        System.out.println("The average of the numbers in the array is : " + avg);   
}//main method