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;

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 // …

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 // …

java.nio.file.Files

Path.of(file)

file.toPath()

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);
        }
    }
}

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');

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
}