Java Chapter 4

Consider this code: "int v = 20; --v; System.out.println(v++);". What value is printed, what value is v left with? Consider this code: "int s = 20; int t = s++ + --s;". What are the values of s and t?

19 is printed, v ends up with 20 s is 20 and t is 40

You are given a String variable named file. It contains the name of a one-line file. Write a sequence of statements that make an exact copy of the file and give it the same name but with the string ".cpy" attached to the filename. Make sure that the data written to the file has been flushed from its buffer and that any system resources used during the course of running these statements have been released.(Do not concern yourself with any possible exceptions here-- assume they are handled elsewhere.)

File f1 = new File(file); Scanner scan = new Scanner(f1); File f2 = new File(file + ".cpy"); PrintWriter pw = new PrintWriter(f2); while(scan.hasNext()){ pw.println(scan.nextLine());} scan.close(); pw.close();

There are two text files, whose names are given by two String variables, file1 and file2. These text files have the same number of lines. Write a sequence of statements that creates a new file whose name consists concatenating the names of the two text files (with a "-" in the middle) and whose contents of merging the lines of the two files. Thus, in the new file, the first line is the first line from the first file, the second line is the first line from the second file. The third line in the new file is the second line in the first file and the fourth line is the second line from the second file, and so on. When finished, make sure that the data written to the new file has been flushed from its buffer and that any system resources used during the course of running your code have been released.(Do not concern yourself with any possible exceptions here-- assume they are handled elsewhere.)

File f1 = new File(file1);File f2 = new File(file2);Scanner wiz1 = new Scanner(f1);Scanner wiz2 = new Scanner(f2);String sFile3 = file1 + "-" + file2;File file3 = new File(sFile3);PrintWriter output = new PrintWriter(file3);while(wiz1.hasNextLine()){output.println(wiz1.nextLine());output.println(wiz2.nextLine());}output.close();output.close();

Given a String variable named line1, write a sequence of statements that use a Scanner to read the first line of a file named "poem" and stores it in line1. (Do not concern yourself with any possible exceptions here-- assume they are handled elsewhere.

File fileInput = new File("poem"); Scanner scan = new Scanner(fileInput); line1 = scan.nextLine();

Given an initialized String variable outfile, write a statement that declares a PrintWriter reference variable named output and initializes it to a reference to a newly created PrintWriter object associated with a file whose name is given by outfile. (Do not concern yourself with any possible exceptions here-- assume they are handled elsewhere.)

PrintWriter output=new PrintWriter(outfile);

Declare a variable logfileName that is suitable for holding the name of a file

String logfileName;

Given a Scanner reference variable named input that has been associated with an input source consisting of a sequence of lines of text and an int variable named count, write the code necessary to count the lines of text in the input source and place that value into count

count = 0; while(input.hasNext()){ input.nextLine(); count++;}

Given an int variable n that has already been declared, write some code that repeatedly reads a value into n until at last a number between 1 and 10 (inclusive) has been entered. ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input

do{ n =stdin.nextInt();} while (n > 10 || n < 1);

Given a String variable response that has already been declared, write some code that repeatedly reads a value from standard input into response until at last a Y or y or N or n has been entered. ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input.

do{response = stdin.next();}while (!response.equals("Y") && !response.equals("y") && !response.equals("N") && !response.equals("n"));

Write a loop that displays all possible combinations of two letters where the letters are 'a', or 'b', or 'c', or 'd', or 'e'. The combinations should be displayed in ascending alphabetical order: aa ab ac ad ae ba bb ... ee

for (char i='a'; i<='e'; i++) for (char j='a'; j<='e'; j++) { System.out.print(i); System.out.println(j);}

Assume that the int variables i and j have been declared, and that n has been declared and initialized. Using for loops (you may need more than one), write code that will cause a triangle of asterisks of size n to be output to the screen.

for (i = 1; i <= n; i++){ for (j = 1; j <= i; j++){ System.out.print("*"); } System.out.println(); }

Write a for loop that prints all the even integers from 80 through 20 inclusive, separated by spaces.

for (int i=80; i>=20; i--){ if ((i % 2)==0) { System.out.print(i + " "); }}

You need to write a loop that will repeat exactly 125 times. Which is the preferred loop construct to use? You need to write a loop that will keep reading and adding integers to a sum, until the sum reaches or exceeds 21. The numbers are all less than 20 and the sum is initially 0. Which is the preferred loop construct to use?

for loop do while loop

Write a for loop that prints in ascending order all the positive multiples of 5 that are less than 175, separated by spaces.

for(int i =1; i<175; i++){ if((i%5) ==0) { System.out.print(i + " "); } }

Write a for loop that prints the integers 0 through 39, separated by spaces.

for(int i=0; i<40; i++){ System.out.print(i+" "); }

Given an int variable k that has already been declared, use a for loop to print a single line consisting of 97 asterisks. Use no variables other than k

for(k=1;k<=97; k++){ System.out.print("*"); }

Given a Scanner reference variable named input that has been associated with an input source consisting of a sequence of lines, write the code necessary to read in every line and print them all out on a single line, separated by a space. There should NOT be a trailing space at the end of the line

if (input.hasNext()) System.out.print(input.nextLine()); while (input.hasNext()){ System.out.print(" " + input.nextLine());}

Write a statement that terminates the current loop when the value of the int variables x. and y.are equal

if (x == y) break;

Distance TraveledThe distance a vehicle travels can be calculated as follows:Distance = Speed * TimeFor example, if a train travels 40 miles-per-hour for three hours, the distance traveled is120 miles. Write a program that asks for the speed of a vehicle (in miles-per-hour) and thenumber of hours it has traveled. Both values are assumed to be integers. It should use aloop to display the distance a vehicle has traveled for each hour of a time period specifiedby the user. For example, if a vehicle is traveling at 40 mph for a three-hour time period,it should display a report similar to the one that follows:Hours Distance Traveled---------------------------1 402 803 120Input Validation: Do not accept a negative number for speed and do not accept any valueless than 1 for time traveled.

import java.util.Scanner; public class DistanceTravelled { public static void main(String[] args) { Scanner in = new Scanner(System.in); int speed, time; System.out.print("Enter vehicle speed (in mph): "); speed = in.nextInt(); System.out.print("Enter time travelled (in hrs): "); time = in.nextInt(); System.out.println("Hour\tDistance Travelled"); System.out.println("--------------------------"); for(int i = 1; i <= time; ++i) { System.out.println(i + "\t\t\t" + (i*speed)); } } }

Write a loop that reads positive integers from standard input, printing out those values that are even, each followed by a space, and that terminates when it reads an integer that is not positive. Declare any variables that are needed. ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input.

int num=1; while (num>0){ num = stdin.nextInt(); if ((num % 2) == 0 && num > 0 ){ System.out.print(num + " ");}}

Write a loop that reads positive integers from standard input and that terminates when it reads an integer that is not positive. After the loop terminates, it prints out, separated by a space and on a single line, the sum of all the even integers read and the sum of all the odd integers read. Declare any variables that are needed. ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input

int odd=0;int even=0;int i=1;while (i>0){i = stdin.nextInt();if ((i % 2)==0 && (i>0)){even+=i;}if ((i % 2)!=0 && (i>0)){odd+=i;}}System.out.print(even + " " + odd);

Given an int variable n that has been initialized to a positive value and, in addition, int variables k and total that have already been declared, use a while loop to compute the sum of the cubes of the first n whole numbers, and store this value in total. Use no variables other than n, k, and total and do not modify the value of n

k = 0; total=0; while(k <= n ){ total = total + (k*k*k) ; k++ ; }

Given an int variable k that has already been declared, use a do...while loop to print a single line consisting of 53 asterisks. Use no variables other than k.

k =53; do{ System.out.print("*"); k--; }while (k >= 1);

Given an int variable k that has already been declared, use a while loop to print a single line consisting of 88 asterisks. Use no variables other than k.

k=0; while( k < 88) { System.out.print("*"); k++; }

Consider this data sequence: "fish bird reptile reptile bird bird bird mammal fish". Let's define a SINGLETON to be a data element that is not repeated immediately before or after itself in the sequence. So, here there are four SINGLETONs (the first appearance of "fish", the first appearance of "bird", "mammal", and the second appearance of "fish"). Write some code that uses a loop to read a sequence of words, terminated by the "xxxxx". The code assigns to the variable n the number of SINGLETONs that were read. (For example in the above data sequence it would assign 4 to n. Assume that n has already been declared. but not initialized. Assume that there will be at least one word before the terminating "xxxxx". ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input.

n = 0; String word1, word2, word3; word3 =stdin.next(); word2 = stdin.next(); word1 = stdin.next(); if (!(word3.equals(word2)))n++;if (!(word2.equals(word3)) && (!(word2.equals(word1))))n++;while (!(word1.equals("xxxxx")) && (stdin.hasNext())){word3 = word2;word2 = word1;word1 = stdin.next();if (!(word2.equals(word3)) && (!(word2.equals(word1))))n++;}

Write an expression whose value is a reference to a newly created PrintWriter object associated with a file named "output.txt". (Do not concern yourself with any possible exceptions here-- assume they are handled elsewhere.)

new PrintWriter("output.txt")

Given an initialized String variable message, and given a PrintWriter reference variable named output that references a PrintWriter object, write a statement that writes the string referenced by message to the file output streams to.

output.print(message);

Given an integer variable strawsOnCamel, write a statement that uses the auto-increment operator to increase the value of that variable by 1.

strawsOnCamel++;

Write a statement that increases the value of the int variable total by the value of the int variable amount. That is, add the value of amount to total and assign the result to total.

total += amount;

Given an int variable n that has been initialized to a positive value and, in addition, int variables k and total that have already been declared, use a for loop to compute the sum of the cubes of the first n whole numbers, and store this value in total. Use no variables other than n, k, and total

total=0; for (k=n;k>0;--k) total = total+ (k*k*k);

Given int variables k and total that have already been declared, use a do...while loop to compute the sum of the squares of the first 50 counting numbers, and store this value in total. Thus your code should put 1*1 + 2*2 + 3*3 +... + 49*49 + 50*50 into total. Use no variables other than k and total.

total=0; k=1; do{ total += k*k; k++;} while (k<=50);