Java BufferedWriter Examples: Write Strings to Text File

Use the BufferedWriter type to create a text file and write strings to it. Call the write and newLine methods.

BufferedWriter. This class helps us write Strings and characters to a file. We can write a String with write(). With newLine() we add a newline.

Arrays, substrings. With BufferedWriter we are not limited to Strings. We can write chars, ints, arrays and even substrings. We often pass a FileWriter to the BufferedWriter constructor.

First example. This program introduces the syntax for BufferedWriter. We create a FileWriter and pass an example path to it. This is the target text file.

Write: We call this method on the BufferedWriter. No newline is inserted afterwards. We can pass a string argument.

NewLine: This inserts a platform-specific newline to the file. Often we call this after a string to create a file with lines.

Close: This finishes the file writing operations. We cannot write any more to the file.

Java program that uses BufferedWriter, write, newLine import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class Program { public static void main(String[] args) throws IOException { // Create a BufferedWriter around a FileWriter. // ... Write to an output text file. BufferedWriter writer = new BufferedWriter(new FileWriter( "C:\\programs\\output.txt")); // Write these lines to the file. // ... We call newLine to insert a newline character. writer.write("CAT"); writer.newLine(); writer.write("DOG"); writer.newLine(); writer.write("BIRD"); writer.close(); } } Output file: output.txt CAT DOG BIRD

Write string array. This example writes an entire String array to a file. It specifies a newline after each String. So we write an array to lines in a file.

Java program that writes String array to file import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class Program { public static void main(String[] args) throws IOException { String[] array = new String[3]; array[0] = "100A"; array[1] = "200B"; array[2] = "300C"; // Create our BufferedWriter. BufferedWriter writer = new BufferedWriter(new FileWriter( "C:\\programs\\output.txt")); // Loop over the elements in the string array and write each line. for (String line : array) { writer.write(line); writer.newLine(); } writer.close(); } } Output file: output.txt 100A 200B 300C

Substrings, chars, ints. BufferedWriter handles more than strings. It can write just a part of a string—a substring (specified with a start index and length).

Char: To write a char, we must use the append method. The write method will not work—it treats chars as integers.

Int: With write we write integers. If we write the ASCII value 97 we see an "a" in the file.

Char array: Write can handle an entire char array. We can also specify just a range within a char array.

Char Arrays

Java program that writes substrings, chars, ints import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class Program { public static void main(String[] args) throws IOException { BufferedWriter writer = new BufferedWriter(new FileWriter( "C:\\programs\\output.txt")); // Write the second two characters of this string. String value = "abcdefghi"; writer.write(value, 2, 2); writer.newLine(); // Append a character to the file. writer.append(value.charAt(1)); writer.newLine(); // Write an integer to the file. writer.write(97); writer.newLine(); // Write a character array. // ... A range of characters can be instead written. char[] array = value.toCharArray(); writer.write(array); // Close our writer. writer.close(); } } Output file: output.txt cd b a abcdefghi

IOException, stream closed. Often the BufferedWriter will throw exceptions. In this example, we get an IOException because we write to a file we had already closed.

Warning: Writing files, as with BufferedWriter, causes many errors. Often exception handling (try, catch) keywords are needed.

Exceptions

Java program that writes after close import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class Program { public static void main(String[] args) throws IOException { BufferedWriter writer = new BufferedWriter(new FileWriter( "C:\\programs\\output.txt")); // Close the writer. writer.close(); // This will cause an exception. writer.write("X"); } } Output Exception in thread "main" java.io.IOException: Stream closed at java.io.BufferedWriter.ensureOpen(Unknown Source) at java.io.BufferedWriter.write(Unknown Source) at java.io.Writer.write(Unknown Source) at Program.main(Program.java:15)

Throws IOException. In the examples, we use the "throws IOException" notation on our main methods. This is required—BufferedReader can cause an error for many reasons.

With BufferedReader, and the FileWriter type as help, we write Strings to file with ease. We can form lines with the newLine method.

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Java BufferedWriter Examples: Write Strings to Text File

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