Practice›Java Fundamentals›Module 6. Input, Files & Error Handling›(Optional) 6.4 Writing files

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(Optional) 6.4 Writing files — PrintWriter basics

Lesson

Optional lesson — beyond the AP CS A exam. Writing to files is not on the AP exam (which only reads files); this is here for a fuller picture of Java.

Writing text output

A PrintWriter writes text, just like System.out. It has print (no line break) and println (adds a line break). After writing, call flush() to make sure everything is sent, or close() when finished.

Worked example

PrintWriter out = new PrintWriter(System.out);
out.println("Line 1");
out.print("No newline ");
out.println("here");
out.flush();

println ends the line; print does not. flush() pushes the text out. Here it writes to the screen; the next lesson writes to a file with the very same methods.

▶ Try it: run this, then add more print/println calls and re-run.

import java.io.PrintWriter;
public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        out.println("Line 1");
        out.println("Line 2");
        out.print("No newline ");
        out.println("here");
        out.flush();
    }
}

Which PrintWriter method adds a line break?

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Why call flush() after writing?

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Type exactly what this program prints.

PrintWriter out = new PrintWriter(System.out);
out.print("Hi ");
out.println("there");
out.println("bye");
out.flush();

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Match each method to what it does.

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True or false?

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