I want to get information from the user like last name, first name, and id number for example Smith, John 12345 and continue looping until the user enters "exit". Whenever I enter two inputs the first one gets wiped out and the second one is stored. Maybe I should be using a different approach then what I have...
InputStreamReader reader = new InputStreamReader(System.in);
BufferedReader input = new BufferedReader(reader);
String inputValues;
String person;
String lastname = "";
String firstname = "";
String id = "";
while(true){
inputValues = input.readLine();
person = inputValues.split("\\s+");
if(inputValues.equals("exit"){
break;
}
else {
lastname = person[0];
firstname = person[1];
id = person[2];
}
}
I know my program is wrong but this is what I have thus far. I do not know how to store multiple people to eventually print out their names and id at the end of this.
I hope I understand your problem correct: your problem is that you overwrite your old entries? To prevent that you have to use some kind of array or list.
import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
public static void main (String[] args) throws java.lang.Exception
{
InputStreamReader reader = new InputStreamReader(System.in);
BufferedReader input = new BufferedReader(reader);
String inputValues;
String[] person;
List<String> lastname = new ArrayList<String>();
List<String> firstname = new ArrayList<String>();
List<String> id = new ArrayList<String>();
while(true){
inputValues = input.readLine();
person = inputValues.split("\\s+");
if(inputValues.equals("exit")){
break;
}else{
lastname.add(person[0]);
firstname.add(person[1]);
id.add(person[2]);
}
}
for(int i=0; i<lastname.size(); i++)
System.out.println(firstname.get(i) +" "+ lastname.get(i) +" ("+ id.get(i) +")");
}
}
See here: https://ideone.com/l1TnF8
Just as kon has noted you need an array of strings for person, what is happening is that each time you input a new value the new one only replaces the old one since person is only a string occupying just one memory space.
Related
just a another noob to Java with a dumb question.
I am trying to create a function that receives a String array and fills it with text input from the user using Bufferedreader (which I currently want to use).
I sort of have the idea in my head but it gives the error cannot find symbol when using the readline() property. How can I achieve this?
public static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
public static void fill_array (String parray []){
for(int i = 0; i < parray.length; i++){
parray[i] = in.readline(); //Here it gives me the error
}
}
readLine() and not readline how embarrasing
Hii Scanner is much more simpler than BufferedReader to read input, Let me give you an example :
import java.util.*;
public class Main
{
public static void main(String arp[])
{
Scanner scanner = new Scanner(System.in);
String address = scanner.nextLine(); // read string with spaces
System.out.println("addres : "+ address);
String name = scanner.next(); // read string without spaces
System.out.println("name : "+ name);
Integer age = scanner.nextInt(); // read Integer input
System.out.println("age : "+ age);
}
}
Scanner java api link : https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
I have a program which reads some data under a file reader and then creates an instance of another class which models the data. Anyway that class works (has been tested with some hard coded values) but I now want to output the data of the instance of a Patient being read under the file reader but seem unable to.
Could anyone tell me where i'm going wrong.
You are not adding Patient instances to newPatient collection, that's why it's empty and you are not getting anything printed out. Add elements to queue:
while(scan.hasNextLine()){
String firstname = scan.nextLine();
String surname = scan.nextLine();
String illness = scan.nextLine();
int illnessSeverity = scan.nextInt();
String newLine = scan.nextLine();
newPatient.add(new Patient(firstname,surname,illness,illnessSeverity));
for (Patient newPatientData : newPatient) {
System.out.println(newPatientData);
}
You need to add data first to the Priority Queue. I think you missed that .
PriorityQueue<Patient> newPatient = new PriorityQueue<>();
File fileName = new File("patients.txt");
Scanner scan = null;
try {
scan = new Scanner(fileName);
while(scan.hasNextLine()){
String firstname = scan.nextLine();
String surname = scan.nextLine();
String illness = scan.nextLine();
int illnessSeverity = scan.nextInt();
String newLine = scan.nextLine();
Patient newP = new Patient(firstname,surname,illness,illnessSeverity);
newPatient.add(newP);
}
for (Patient newPatientData : newPatient) {
System.out.println(newPatientData);
}
} catch(Exception e) {
System.out.println("ERROR - file not found");
}
I have a csv file like this:
"user1","track1","player1"
-------------------------
"user1","track2","player2"
-------------------------
"user1","track3","player3"
-------------------------
"user1","track4","player4"
-------------------------
"user2","track2","player3"
-------------------------
.
.
"userN","trackM","playerX"
What I need to do is to divid tracks and players related to each user into a half and put them in separate files.
For example, for user1, if it has 4 lines, I need to divid it into two parts (the first two lines in file A, and the rest in file B), and repeating the same action for all users.
This is what I wrote so far:
public static void main(String[] args) throws java.lang.Exception {
BufferedReader userlines = new BufferedReader(new FileReader("/Users/mona/Documents/Bolzano/Datasets/Lastfm_Matthias/lastfm_usertrackplayer.csv"));
String uLine = null;
while ((uLine = userlines.readLine()) != null) {
String[] userId = uLine.split(",");
ArrayList<String> list = new ArrayList<String>();
list.add(uLine);
for(int i=0; i<=list.size();i++){
// --> THIS FOR CONDITION IS MY PROBLEM,I need s.th like for(i=0; i<=(last unique userId (i.e., length of userId[i]) until it reaches the next unique userId)
//Divide the lines and put into two separate files
}
}
userlines.close();
}
Sorry I know it should be something simple, but I really could not find any related/similar question by googling my problem :(
Could someone help me please?
Thanks
You cannot know "a priori" the number of lines for each user.
So you must memorize (in a List for example) all lines for the current user until you read the next user. Then save, in both files, the content of the list.
Clean the list, do the same thing for the next user.
EDIT
public static void main(String[] args) throws java.lang.Exception {
try(BufferedReader userlines = new BufferedReader(new FileReader("/Users/mona/Documents/Bolzano/Datasets/Lastfm_Matthias/lastfm_usertrackplayer.csv"));) {
String uLine = null;
ArrayList<String> list = new ArrayList<String>();
String currentUserId = null;
while ((uLine = userlines.readLine()) != null) {
String[] userData = uLine.split(",");
String userId = userData[0]; // <-- get User ID here
if (userId.equals(currentUserId)) {
// Do what ever you need while buffering same userId
} else {
// Save currentUserId in file
yourSaveMethod(list);
currentUserId = userId;
list.clear();
}
list.add(uLine);
}
}
}
You can use StringTokenizer class for parsing data.
Example:
String str = "user1, track1, player1";
StringTokenizer st = new StringTokenizer(str);
System.out.println("---- Split by space ------");
while (st.hasMoreElements()) {
System.out.println(st.nextElement());
}
System.out.println("---- Split by comma ',' ------");
StringTokenizer st2 = new StringTokenizer(str, ",");
while (st2.hasMoreElements()) {
System.out.println(st2.nextElement());
}
I'm fairly new to programming and I recently wrote something to utilize a scanner class to fill an object array from a text file. Essentially, I can re-write this text file or add new info and won't have to change the code. I suppose my question is this: is there an easier/more preferred method to doing this? I'm trying to learn the coding nuances.
import java.io.*;
import java.util.*;
public class ImportTest {
public static void main(String[] args) throws IOException
{
Scanner s = null;
Scanner k = null;
ArrayList myList = new ArrayList<String>();
ArrayList myList2 = new ArrayList<String>();
ArrayList myList3 = new ArrayList<Student>();
try
{
s = new Scanner(new BufferedReader(new FileReader("testMe.txt")));
while (s.hasNext())
{
myList.add(s.nextLine());
}
}
finally
{
if (s != null)
{
s.close();
}
}
System.out.println("My List 1:");
for(int i=0; i<myList.size(); i++)
{
System.out.println(i+". "+myList.get(i));
}
for(int x=0; x<myList.size(); x++)
{
try
{
k = new Scanner(myList.get(x).toString());
while (k.hasNext())
{
myList2.add(k.next());
}
}
finally
{
if (k != null)
{
k.close();
}
}
String name;
int age;
double money;
name=myList2.get(0).toString();
age=Integer.parseInt(myList2.get(1).toString());
money=Double.parseDouble(myList2.get(2).toString());
Student myStudent=new Student(name, age, money);
myList3.add(myStudent);
myList2.clear();
}
System.out.println("Test of list object: ");
for(int i=0; i<myList3.size(); i++)
{
System.out.println(i+". "+myList3.get(i).toString());
}
}
}
I would read the file line by line and parse every line directly. This way you do not need 3 lists, 2 scanners and multiple iterations:
String line = "";
BufferedReader br = new BufferedReader(new FileReader("test.txt"));
ArrayList<Student> students = new ArrayList<Student>();
while( (line = br.readLine()) != null)
{
String[] tmp = line.split("\\s+"); //split line by spaces
//this needs bounds & error checking etc.
students.add(new Student(tmp[0], Integer.parseInt(tmp[1]), Double.parseDouble(tmp[2])));
}
In Java 7 you can use the new file functions to read all lines at once:
List<String> allLines = Files.readAllLines("test.txt", Charset.defaultCharset());
Do not forget to close the reader or use try-with-resources (since java 1.7)
Correct me if I am wrong, testMe.txt file contains Student information which are name, age, money, and you want read those values.
Best way to do it is you should serialize your Student objects into the the testMe.txt with the help of ObjectOutputStream. As well you can read those value using ObjectInputStream, so in this way you can able to get Student objects itself(no need to hnadle String).
In case you do want to serialize the data into file, you should store the data in some predefined format like as comma(,) or semi-colon(;) seperated.
For Example -
emp1, 24, 20000
emp emp2, 25, 24000
emp3, 26, 26000
In this case while reading the string you can split it with seperation character and get the actual information.
Code snippet:
List<Student> students = new ArrayList<Student>();
...
try(scanner = new Scanner(new BufferedReader(new FileReader("testMe.txt")))){
while (scanner.hasNext()){
String data[] = scanner.nextLine().split(",");
Student student = new Student(data[0],data[1],data[2]);
students.add(student);
}
}
Try-with-resource will automatically handle the resouce, you dont need to explicitly close it. This features available in java since 1.7.
i am doing a self project to help me understand more about java.but i am stuck at this question.
I have a following txt file :
Name Hobby
Susy eat fish
Anna gardening
Billy bowling with friends
What is the best way to read all the line and put it in arraylist(name,hobby). but the tricky part is the
eat fish or bowling with friends
has white spaces and it must be put under one array and obviously i cannot hardcode it.
here is my current code
public void openFile(){
try{
x = new Scanner(new File("D://practice.txt"));
}catch (Exception e){
System.out.println("File could not be found");
}
}
public void readFile(){
while (x.hasNextLine()){
x.nextLine();
if (x.hasNext()){
listL.add(x.next());
} else {
listL.add("");
}
if (x.hasNext()){
listR.add(x.next());
} else {
listR.add("");
}
}
}
thanks in advance...
note = 1.hobby and name are separated by spaces
2.names will only have one word only
Instead of doing scanner.next(), you may want to do something like this:
Scanner scan = new Scanner(new File("D://practice.txt"));
ArrayList<String> names = new ArrayList<String>();
ArrayList<String> hobbies = new ArrayList<String>();
while(scan.hasNext()){
String curLine = scan.nextLine();
int indexOfHobby = curLine.indexOf(' ');
names.add(curLine.substring(0, indexOfHobby).trim());
hobbies.add(curLine.substring(indexOfHobby).trim());
}
One problem with this is that there is no relationship between the two ArrayLists, so you have to be sure to mind your indices as you iterate through. One way to fix this would be to add a Person class so that you can have name and hobby as attributes of Person, then have an ArrayList of Persons. That might look like this:
Class Person {
String name;
String hobby;
public Person(String name, String hobby){
this.name = name;
this.hobby= hobby;
}
// more methods here
}
Then, in your main class, you'd do this:
Scanner scan = new Scanner(new File("D://practice.txt"));
ArrayList<Person> people= new ArrayList<Person>();
while(scan.hasNext()){
String curLine = scan.nextLine();
int indexOfHobby = curLine.indexOf(' ');
people.add(new Person(curLine.substring(0, indexOfHobby).trim(), curLine.substring(indexOfHobby).trim() ));
}
Also consider using a Map<String,String> to store people with their hobby together instead of keeping two different structures:
Scanner scan = new Scanner(new File("D://practice.txt"));
Map<String,String> namesAndHobbies = new HashMap<String,String>();
while(scan.hasNext()){
String line = scan.nextLine();
int idx = line.indexOf(' ');
String name = line.substring(0, idx).trim();
String hobby = line.substring(idx).trim();
namesAndHobbies.put(name, hobby);
}
This will allow you to access people by name, so you can find out the hobby of a person by name.
Use namesAndHobbies.keySet() to get a collection of all names and namesAndHobbies.values() to get a collection of all hobbies.