CS 101-01 Quizzes

Date: Feb. 14, 2017
Question a) Which of the following are not valid identifiers? Explain.
```
	myClass
	class
	6ab
	int
	main
	[ab]
	%a
	ab+7
	Class
	(7)
```
Answer:
class: reserved word.
6ab: starts with a digit.
int: reserved word.
[ab]: contains "[" and "]"
%a: contains "%"
ab+7: contains "+"
(7): contains "(" and ")"

Question b) What is the output of the following program?
```
public class Q1 {
	public static void main (String[] args) {
		int a = 3;
		int b = a + 4;
		b = b + a;
		System.out.println(b);
	}
}
```
Answer: 10
Date: Mar. 21, 2017
Question: Body Mass Index (BMI) is defined as weight / height², where weight is in kg and height is in m.
Write a method that returns the BMI of a person. It takes the weight and height in kg and m, respectively. Assume that the actual parameters have valid values.
A simple call would be
```
	aBMI = bmi(81.2, 1.73);
```
Answer:
```
	/**
	* Computes the BMI of a person
	* @param weight the weight of the person, in kg
	* @param height the height of the person, in m
	* @return the BMI
	*/
	public static double bmi(double weight, double height) {
		return weight/height/height;
	} // bmi
```

Date: Mar. 23, 2017
Question: Write a method, called countDigits, that takes a string argument, and returns the number of digits in the argument. Write its javadoc comments, as well.

For example, for the string "ab7Ag627", it returns 4.
Answer:

	/**
	 * Counts the number of digits in a string
	 * @param str the string
	 * @return the number of digits in a str
	 */
	public static int countDigits(String str) {
		int count = 0;
		for (int i=0; i < str.length(); i++)
			if (Character.isDigit(str.charAt(i)))
				count++;
		return count;
	} // countDigits

Date: Mar. 30, 2017
Question: Write a method, called initializeIntArray, that takes two arguments; the first arguments is and int[] and the second is int. This method sets the value of each element of the array to the second argument. Write its javadoc comment, also.
Answer:

	/**
	* Sets the value of each element of the array to the second argument.
	* @param array, array to be initialized
	* @param value, to be the value of each element
	*/
	public static void initializeIntArray(int[] array, int value) {
		for (int i=0; i < array.length; i++)
			array[i] = value;
	} // initializeIntArray

A sample call:

	public static void main(String[] args) {
		int[] a = new int[10];
		initializeIntArray(a, 5);
	}

Date: Apr. 13, 2017
Question:Class Watch is defined as below:

public class Watch {
	private boolean digital;
	private static int hours = 12;
	private int minutes;
	private String color = "Gray";
	
	public Watch (){
	}
	
	public Watch (int hours){
		this.hours = hours;
	}
	
	public Watch (int hours, int minutes){
		this.hours = hours;
		this.minutes = minutes;
	}
	
	public Watch (String color){
		this.color = color;
	}
		
	public int getHours () {
		return hours;
	} // getHours
	
	public void setHours(int hours) {
		this.hours = hours;
	} // setHours
	
	public int getMinutes () {
		return minutes;
	} // getMinutes
	
	public void setMinutes(int minutes) {
		this.minutes = minutes;
	} // setMinutes
	
	public String getColor () {
		return color;
	} // getColor
	
	public void setColor(String color) {
		this.color = color;
	} // setColor
} // Watch

What is the output of the following code segment?

	public static void main(String[] args) {
		Watch myW1 = new Watch(1, 2);
		Watch yourW1 = new Watch(3);
		Watch herW1 = new Watch("Pink");
		System.out.println(myW1.getHours()+" "+myW1.getMinutes());
		System.out.println(yourW1.getHours()+" "+yourW1.getMinutes());
		System.out.println(herW1.getHours()+" "+herW1.getMinutes());
	}

Answer:

3 2
3 0
3 0

Date:May 2, 2017
Question:Write a complete program that opens a text file whose name is "original.txt", and creates its copy into a file whose name is "copy.txt".
Answer:

import java.util.Scanner;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;

public class Q6_1 {

	public static void main(String[] args) throws IOException {
        File inFile = new File ("original.txt");
        Scanner in = new Scanner (inFile);
        PrintWriter out = new PrintWriter ("copy.txt");
        String line;
        while (in.hasNextLine()) {
        	line = in.nextLine();
        	out.println(line);
        } // while
        in.close();
        out.close();
	} // main
} // class  Q6_1

Date:May 4, 2017
Question:What is the output of the following program?

import java.util.Scanner;
public class Quiz7_1 {

	public static void main(String[] args) {
		String text1 = "123";
		Scanner sc1 = new Scanner(text1);
		sc1.useDelimiter("");
		while (sc1.hasNext()) System.out.println(sc1.next());
		String text2 = "12 abr \t 12.75 false \n ABC";
		Scanner sc2 = new Scanner(text2);
		while (sc2.hasNext())
			if(sc2.hasNextDouble())
				System.out.println(2 * Double.parseDouble(sc2.next()));
			else
				System.out.println(sc2.next());
	} // main()
} // class

Answer:

1
2
3
24.0
abr
25.5
false
ABC

Date:May 9, 2017
Question:Write a program that takes any number of integers from the command line and displays their sum.
Answer:

public class Sum {
	public static void main(String[] args) {
		int sum =0;
		for (String a: args)
			sum += Integer.parseInt(a);
		System.out.println(sum);
	} // main()
}