テキストファイルの内容を行番号の情報とともに格納するJavaクラス

TargetFile.java

import org.jetbrains.annotations.NotNull;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public class TargetFile {
    @NotNull
    public final String name;
    @NotNull
    public final String content;

    public TargetFile(@NotNull String name, @NotNull String content) {
        this.name = name;
        this.content = content;
    }

    public TargetFile(@NotNull Path path) throws IOException {
        this.name = path.toFile().toString();
        this.content = new String(Files.readAllBytes(path));
    }
}

TargetFileWithLineNumber.java

import org.jetbrains.annotations.NotNull;

import java.io.IOException;
import java.nio.file.Path;
import java.util.Arrays;

public class TargetFileWithLineNumber extends TargetFile {
    @NotNull
    private final int[] lineEnds;

    public TargetFileWithLineNumber(@NotNull String name, @NotNull String content) {
        super(name, content);
        this.lineEnds = getLineSeparators(this.content);
    }

    public TargetFileWithLineNumber(@NotNull Path path) throws IOException {
        super(path);
        this.lineEnds = getLineSeparators(this.content);
    }

    @NotNull
    private static int[] getLineSeparators(@NotNull String content) {
        int[] array = new int[256];
        int index = 0;
        int pos = 0;
        while ((pos = content.indexOf('\n', pos)) != -1) {
            if (index - 1 >= array.length) {
                array = Arrays.copyOf(array, array.length * 2);
            }
            array[index++] = pos++;
        }
        return Arrays.copyOf(array, index);
    }

    public int getLineNumber(int i) {
        int index = Arrays.binarySearch(this.lineEnds, i);
        return index < 0 ? -index : index + 1;
    }

    public int getLineStart(int i) {
        return i == 1 ? 0 : this.lineEnds[i - 2] + 1;
    }

    public int getLineEnd(int i) {
        return this.lineEnds.length == i ? this.content.length() - 1 : this.lineEnds[i - 1];
    }

    public int getLineSize() {
        return this.lineEnds.length;
    }
}