This site requires JavaScript, please enable it in your browser!
Greenfoot back
Twitter Twitter.hover
Darkstep
Darkstep wrote ...

2021/6/22

How to read and use a text file?

Darkstep Darkstep

2021/6/22

#
So what I want to be able to do is access a text file where I've written lines of addObjects that the world can use to add objects at those coordinates. I've seen some scanner methods but I don't know how to implement them and use them like I want to. Any code will help, thanks!
RcCookie RcCookie

2021/6/22

#
Disclaimer: this will not work online! How to read a (text) file Read the whole file into a string array:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
import java.io.File;
import java.io.IOException;
import java.nio.Files;
import java.nio.Path;
 
// —-
 
File file = new File(„files/someFile.someSuffix“);
String[] lines;
try {
    lines = Files.readLines(Path.of(file)); // You can also pass the path string from above directly instead of the file object
} catch(IOException e) {
    System.err.println(„An exception occurred while reading the file “ + file);
}
 
// Example if you don’t know how to use arrays
String firstLine = lines[0];
int lineCount = lines.length;
Read a file character by character or line by line:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
 
// —-
 
File file = new File(…);
try {
    Scanner sc = new Scanner(file);
    while(sc.hasNext()) {
        char next = sc.next();
        // do something with it
    }
     
    // Alternatively
    while(sc.hasNext()) {
        String line = sc.nextLine();
        // …
    }
} catch // …
How to write text into a file
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
import java.io.File;
import java.io.IOException
import java.io.PrintWriter;
 
// —-
 
File file = new File(…);
 
// Create file and directories
new File(file.getParent()).mkDirs();
file.createNewFile();
 
// Write into file
try(PrintWriter writer = new PrintWriter(file)) {
    writer.printLn(„Hello World!“);
    // PrintWriter is similar to the default output stream „System.out“ / „System.err“, and has the same methods like print or printLn
} catch // …
RcCookie RcCookie

2021/6/22

#
Also you can name your File however you want, you may name it „.txt“, you may name it „.json“ or „.someWeirdSuffixThatDoesNotMakeSence“. The suffix is just a name and used by the OS to identify a program to use the file with. It has nothing to do with encoding. You can even leave the suffix away completely.
Darkstep Darkstep

2021/6/22

#
RcCookie wrote...
Disclaimer: this will not work online! How to read a (text) file Read the whole file into a string array:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
import java.io.File;
import java.io.IOException;
import java.nio.Files;
import java.nio.Path;
 
// —-
 
File file = new File(„files/someFile.someSuffix“);
String[] lines;
try {
    lines = Files.readLines(Path.of(file)); // You can also pass the path string from above directly instead of the file object
} catch(IOException e) {
    System.err.println(„An exception occurred while reading the file “ + file);
}
 
// Example if you don’t know how to use arrays
String firstLine = lines[0];
int lineCount = lines.length;
Read a file character by character or line by line:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
 
// —-
 
File file = new File(…);
try {
    Scanner sc = new Scanner(file);
    while(sc.hasNext()) {
        char next = sc.next();
        // do something with it
    }
     
    // Alternatively
    while(sc.hasNext()) {
        String line = sc.nextLine();
        // …
    }
} catch // …
How to write text into a file
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
import java.io.File;
import java.io.IOException
import java.io.PrintWriter;
 
// —-
 
File file = new File(…);
 
// Create file and directories
new File(file.getParent()).mkDirs();
file.createNewFile();
 
// Write into file
try(PrintWriter writer = new PrintWriter(file)) {
    writer.printLn(„Hello World!“);
    // PrintWriter is similar to the default output stream „System.out“ / „System.err“, and has the same methods like print or printLn
} catch // …
Thanks but when I'm importing the stuff needed, it says for both Files and Path; cannot find symbol - class Files/Path
RcCookie RcCookie

2021/6/22

#
I’m sorry, it’s actually
?
1
java.nio.file.Files
You actually don’t need Path which is also in that package, just replace
?
1
Path.of(file)
with
?
1
file.toPath()
Darkstep Darkstep

2021/6/22

#
RcCookie wrote...
I’m sorry, it’s actually
?
1
java.nio.file.Files
You actually don’t need Path which is also in that package, just replace
?
1
Path.of(file)
with
?
1
file.toPath()
I've imported everything and changed the stuff but although that part's fixed now, for readLines it shows an error that says; cannot find symbol - method readLines(java.nio.file.Path). This is my code as of now:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
import greenfoot.*;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
 
public class MyWorld extends World {
public void readFile() {       
        File file = new File("grid.txt");
        String[] lines;
        try {
            lines = Files.readLines(file.toPath());
        } catch(IOException e) {
            System.err.println("An exception occurred while reading the file " + file);
        }
    }
}
RcCookie RcCookie

2021/6/23

#
Sorry for the mistakes, I was just writing from what I remembered - aparently some wrong stuff. Here's how the reading actually works:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
File file = // ...
List<String> lines;
try {
    lines = Files.readAllLines(file.toPath());
} catch // ...
 
// To convert list to array
String[] linesArray = lines.toArray(new String[0]);
 
// Or simply use the list directly
String firstLine = lines.get(0);
int linesCount = lines.size();
 
// Finally, you can also convert the list to a single string with newlines
import java.util.stream.Collectors;
// ---
String string = lines.stream().collect(Collectors.joining('\n');
Darkstep Darkstep

2021/6/23

#
RcCookie wrote...
Sorry for the mistakes, I was just writing from what I remembered - aparently some wrong stuff. Here's how the reading actually works:
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
File file = // ...
List<String> lines;
try {
    lines = Files.readAllLines(file.toPath());
} catch // ...
 
// To convert list to array
String[] linesArray = lines.toArray(new String[0]);
 
// Or simply use the list directly
String firstLine = lines.get(0);
int linesCount = lines.size();
 
// Finally, you can also convert the list to a single string with newlines
import java.util.stream.Collectors;
// ---
String string = lines.stream().collect(Collectors.joining('\n');
Nice, it works thanks! Sorry for more questions but for the writing in the text file portion it says for file.createNewFile(); unreported exception; must be caught or declared to be thrown.
RcCookie RcCookie

2021/6/23

#
Just put it into a try/catch block like the other times and catch an IOException. Orexpand the existing one:
?
1
2
3
4
5
6
7
8
9
10
11
12
try {
    file.createNewFile();
    PrintWriter writer = new PrintWriter(file);
 
    // Write something to the file
 
    // This was done automatically before because we used the „try-with-resources“ try/catch
    // before. Since the file first has to be created we would now have to close it ourself
    writer.close();
} catch(IOException e) {
    e.printStackTrace(); // Actually a better way of working with an exception
}
Also it’s fine, feel free to keep asking. Not the best explanation by me with all the mistakes.
You need to login to post a reply.