Applied Programming/Lists and Tuples/Java
lists.java
[edit | edit source]/**
* This program demonstrates file and list processing.
*
* It creates a temporary file, adds data to the file, and reads the file
* into a list of lists. It then provides a menu of options for displaying
* and searching the file data.
*
* It will not run if the file already exists.
*
* Input:
* None
*
* Output:
* A temporary file and file contents.
*
* References:
* https://www.tutorialspoint.com/java/java_list_interface.htm
* https://www.tutorialspoint.com/java/java_builtin_exceptions.htm
* https://www.tutorialspoint.com/javaexamples/string_compare.htm
*/
import java.util.*;
/**
* Runs main program logic.
*/
class Main {
public static void main(String[] args) {
String FILENAME = "~file.txt";
if(fileExists(FILENAME)) {
System.out.println("File already exists.\n");
System.exit(1);
}
createFile(FILENAME);
List temperatures = readFile(FILENAME);
deleteFile(FILENAME);
while (true) {
int choice = getChoice();
switch (choice) {
case 1:
displayTemperatures(temperatures, "Celsius");
break;
case 2:
displayTemperatures(temperatures, "Fahrenheit");
break;
case 3:
searchTemperatures(temperatures, "Celsius");
break;
case 4:
searchTemperatures(temperatures, "Fahrenheit");
break;
default:
throw new RuntimeException(
"Invalid option selected");
}
}
}
/**
* Creates filename and adds temperature data to the file.
*
* @param filename
*
* Catches IOException and terminates the program.
*/
private static void createFile(String filename) {
try {
java.io.File file = new java.io.File(filename);
java.io.BufferedWriter writer =
new java.io.BufferedWriter(new java.io.FileWriter(file));
float c;
float f;
writer.write("C,F\n");
for(c = 0; c <= 100; c += 10) {
f = c * 9 / 5 + 32;
writer.write(c + "," + f + "\n");
}
writer.close();
}
catch(java.io.IOException e) {
e.printStackTrace();
System.exit(2);
}
}
/**
* Reads filename and displays each line.
*
* @param filename
* @return temperatures
*
* Catches IOException and terminates the program.
*/
private static List readFile(String filename) {
try {
java.io.File file = new java.io.File(filename);
java.io.BufferedReader reader =
new java.io.BufferedReader(new java.io.FileReader(file));
String line;
line = reader.readLine();
if (!line.trim().equals("C,F")) {
throw new RuntimeException(
"Invalid header format found in " +
filename + ": " + line);
}
List temperatures = new ArrayList();
while(true) {
line = reader.readLine();
if (line == null) {
break;
}
String fields[] = line.trim().split(",");
if (fields.length != 2) {
throw new RuntimeException(
"Invalid record format found in " +
filename + ": " + line);
}
List record = new ArrayList();
record.add(Float.parseFloat(fields[0]));
record.add(Float.parseFloat(fields[1]));
temperatures.add(record);
}
reader.close();
if (temperatures.size() == 0) {
throw new RuntimeException(
"No data found in " +
filename);
}
return temperatures;
}
catch(java.io.IOException e) {
e.printStackTrace();
System.exit(3);
return null;
}
}
/**
* Deletes filename.
*
* @param filename
*/
private static void deleteFile(String filename) {
java.io.File file;
file = new java.io.File(filename);
file.delete();
}
/**
* Determines whether or not filename exists.
*
* @param filename
*
* @return true or false
*/
private static boolean fileExists(String filename) {
java.io.File file;
file = new java.io.File(filename);
return file.exists();
}
/**
* Displays menu and gets choice.
*
* @return choice
*
* Exits:
* If no choice is entered.
*/
private static int getChoice() {
Scanner scanner = new Scanner(System.in);
String text = "";
while (true) {
try {
System.out.println("Select from the following options or press <Enter> to quit:");
System.out.println("1. Display table sorted by Celsius temperature.");
System.out.println("2. Display table sorted by Fahrenheit temperature.");
System.out.println("3. Search for Celsius temperature.");
System.out.println("4. Search for Fahrenheit temperature.");
text = scanner.nextLine();
if (text.isEmpty()) {
System.exit(0);
}
int choice = Integer.parseInt(text);
if (choice >= 1 && choice <= 4) {
System.out.println();
return choice;
}
System.out.println(text + " is not a valid choice.\n");
}
catch (NumberFormatException exception) {
System.out.println(text + " is not a valid choice.\n");
}
}
}
/**
* Sorts temperature list in ascending order by the given element.
*
* @param temperatures
* @param element
* @return temperatures
*/
private static void sortTemperatures(List temperatures, int element)
{
Collections.sort(temperatures, new Comparator<List>() {
@Override
public int compare(List l1, List l2) {
Float f1 = (Float)l1.get(element);
Float f2 = (Float)l2.get(element);
if (f1 > f2) {
return 1;
}
else {
return -1;
}
}
});
}
/**
* Displays temperatures sorted in scale order.
*
* @param temperatures
* @param scale
* @throws IllegalArgumentException if scale is invalid
*/
private static void displayTemperatures(List temperatures, String scale) {
int first_column = 0;
int second_column = 1;
if (scale == "Celsius") {
sortTemperatures(temperatures, 0);
System.out.println("C\tF");
}
else if (scale == "Fahrenheit") {
sortTemperatures(temperatures, 1);
System.out.println("F\tC");
first_column = 1;
second_column = 0;
}
else {
throw new IllegalArgumentException("scale must be Celsius or Fahrenheit");
}
for(int i = 0; i < temperatures.size(); i++){
List record = (List)temperatures.get(i);
System.out.println(record.get(first_column) + "\t" + record.get(second_column));
}
System.out.println();
}
/**
* Gets Fahrenheit or Celsius temperature.
*
* @param scale
* @return temperature
* @throws IllegalArgumentException if no temperature is entered.
*/
private static float getTemperature(String scale) {
assert scale == "Fahrenheit" || scale == "Celsius";
Scanner scanner = new Scanner(System.in);
while (true) {
System.out.println("Enter " + scale + " temperature:");
String text = scanner.nextLine();
if (text.isEmpty()) {
throw new IllegalArgumentException("No temperature entered");
}
try {
float temperature = Float.parseFloat(text);
System.out.println();
return temperature;
}
catch (NumberFormatException exception) {
System.out.println(text + " is not a valid " + scale + " temperature\n");
}
}
}
/**
* Search temperatures for a scale temperature and display the nearest match.
*
* @param temperatures
* @param scale
* @throws IllegalArgumentException if scale is invalid
*/
private static void searchTemperatures(List temperatures, String scale) {
float temperature = 0;
int searchElement = 0;
int displayElement = 1;
String otherScale = "Fahrenheit";
try {
temperature = getTemperature(scale);
}
catch (Exception exception) {
return;
}
if (scale == "Celsius") {
// Use default values
}
else if (scale == "Fahrenheit") {
searchElement = 1;
displayElement = 0;
otherScale = "Celsius";
}
else {
throw new IllegalArgumentException("scale must be Celsius or Fahrenheit");
}
sortTemperatures(temperatures, searchElement);
List last = (List)temperatures.get(0);
List record = null;
for(int i = 0; i < temperatures.size(); i++){
record = (List)temperatures.get(i);
if (temperature < (Float)record.get(searchElement))
{
break;
}
last = record;
}
if (temperature < (Float)last.get(searchElement)) {
System.out.println(String.format(
"%.1f° %s is less than %.1f° %s\n",
temperature,
scale,
last.get(displayElement),
otherScale));
}
else if (temperature == (Float)last.get(searchElement)) {
System.out.println(String.format(
"%.1f° %s is %.1f° %s\n",
temperature,
scale,
last.get(displayElement),
otherScale));
}
else if (temperature > (Float)record.get(searchElement)) {
System.out.println(String.format(
"%.1f° %s is greater than %.1f° %s\n",
temperature,
scale,
last.get(displayElement),
otherScale));
}
else {
System.out.println(String.format(
"%.1f° %s is between %.1f° %s and %.1f %s\n",
temperature,
scale,
last.get(displayElement),
otherScale,
record.get(displayElement),
otherScale));
}
}
}
Try It
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