I can't remember the text file input / output in Java, so I summarized it.

For some reason, every time a project changes, so does the programming language used. Every time, I google how the text file was input and output. The current site is Java, so let's summarize it!

Read

• The value of an externally defined variable in a lambda expression cannot be changed.
• However, it is an unclear mechanism that an array can be rewritten.
• [Reference] Why can I change the value of the array defined outside with a lambda expression

final String baseDir = "/Users/yasuhiro/Documents/tmp";
File f = new File(baseDir + "/timestamp.txt");
StringBuffer sb = new StringBuffer();
String[] lineSeparator = { "" };
BufferedReader br = new BufferedReader(new FileReader(f));
br.lines().forEach(line -> {
	sb.append(lineSeparator[0]);
	sb.append(line);
	lineSeparator[0] = System.lineSeparator();
});
br.close();

• I also made an improved version.

final String baseDir = "/Users/yasuhiro/Documents/tmp";
File f = new File(baseDir + "/timestamp.txt");
StringBuffer sb = new StringBuffer();
String[] lineSeparator = { "" };
try (BufferedReader br = new BufferedReader(new FileReader(f));) {
	br.lines().forEach(line -> {
		sb.append(lineSeparator[0]);
		sb.append(line);
		lineSeparator[0] = System.lineSeparator();
	});
} catch (Exception e) {
	e.printStackTrace();
}

writing

final String baseDir = "/Users/yasuhiro/Documents/tmp";
File f = new File(baseDir + "/timestamp.txt");
BufferedWriter bw = new BufferedWriter(new FileWriter(f));
lines.forEach(line -> {
	try {
		bw.write(line);
		bw.newLine();
	} catch (IOException e) {
		e.printStackTrace();
	}
});
bw.close();

• revised edition. You don't have to write a close
• Finally, the catch part has increased, so it is easier to see before modification.
• So, haven't you improved? !!

final String baseDir = "/Users/yasuhiro/Documents/tmp";
File f = new File(baseDir + "/timestamp.txt");
try (BufferedWriter bw = new BufferedWriter(new FileWriter(f));) {
	lines.forEach(line -> {
		try {
			bw.write(line);
			bw.newLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
	});
} catch (IOException e) {
	for (Throwable t : e.getSuppressed()) {
		t.printStackTrace();
	}
}