Java : PrintWriter - API Examples

PrintWriter (Java SE 18 & JDK 18) API Examples.
You will find code examples on most PrintWriter methods.


Summary

Prints formatted representations of objects to a text-output stream. This class implements all of the print methods found in PrintStream.

Class diagram

final var sw = new StringWriter();
try (final var writer = new PrintWriter(sw)) {
    writer.println("abc");
    writer.printf("num = %d", 1234);
}

System.out.println(sw);

// Result
// ↓
//abc
//num = 1234

Fields

protected Writer out

The underlying character-output stream of this PrintWriter.

protected. I think it's rare to create a subclass of PrintWriter. Therefore, the code example is omitted.

Fields declared in Writer

lock

Please see the link below.

Constructors

PrintWriter (File file)

Creates a new PrintWriter, without automatic line flushing, with the specified file.

final var file = Path.of("R:", "java-work", "sample.txt");

try (final var writer = new PrintWriter(file.toFile())) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file));

// Result
// ↓
//abc
//1234
//○△×

PrintWriter (File file, String csn)

Creates a new PrintWriter, without automatic line flushing, with the specified file and charset.

System.out.println("default charset : " + Charset.defaultCharset());

final var file = Path.of("R:", "java-work", "sample.txt");
final var csn = "Shift_JIS";

System.out.println("-- write --");
try (final var writer = new PrintWriter(file.toFile(), csn)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file, Charset.forName(csn)));

// Result
// ↓
//default charset : UTF-8
//-- write --
//abc
//1234
//○△×

PrintWriter (File file, Charset charset)

Creates a new PrintWriter, without automatic line flushing, with the specified file and charset.

System.out.println("default charset : " + Charset.defaultCharset());

final var file = Path.of("R:", "java-work", "sample.txt");
final var charset = Charset.forName("Shift_JIS");

System.out.println("-- write --");
try (final var writer = new PrintWriter(file.toFile(), charset)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file, charset));

// Result
// ↓
//default charset : UTF-8
//-- write --
//abc
//1234
//○△×

PrintWriter (OutputStream out)

Creates a new PrintWriter, without automatic line flushing, from an existing OutputStream.

final var out = new ByteArrayOutputStream();
try (final var writer = new PrintWriter(out)) {
    writer.println("abc");
    writer.println(1234);
}

System.out.println(out);

// Result
// ↓
//abc
//1234

PrintWriter (OutputStream out, boolean autoFlush)

Creates a new PrintWriter from an existing OutputStream.

// autoFlush = false

final var out = new ByteArrayOutputStream();
try (final var writer = new PrintWriter(out, false)) {

    writer.print("abc");
    System.out.println(out.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.println("XYZ");
    System.out.println(out.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.printf("num = %d", 1234);
    System.out.println(out.toString().isEmpty());

    // Result
    // ↓
    //true
}

System.out.println(out);

// Result
// ↓
//abcXYZ
//num = 1234
// autoFlush = true

final var out = new ByteArrayOutputStream();
try (final var writer = new PrintWriter(out, true)) {

    writer.print("abc");
    System.out.println(out.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.println("XYZ");
    System.out.println(out);

    // Result
    // ↓
    //abcXYZ

    writer.printf("num = %d", 1234);
    System.out.println(out);

    // Result
    // ↓
    //abcXYZ
    //num = 1234
}

System.out.println(out);

// Result
// ↓
//abcXYZ
//num = 1234

PrintWriter (OutputStream out, boolean autoFlush, Charset charset)

Creates a new PrintWriter from an existing OutputStream.

Please see also : PrintWriter(OutputStream out, boolean autoFlush)

System.out.println("default charset : " + Charset.defaultCharset());

final var out = new ByteArrayOutputStream();
final var charset = Charset.forName("Shift_JIS");

System.out.println("-- write --");
try (final var writer = new PrintWriter(out, false, charset)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(out.toString(charset));

// Result
// ↓
//default charset : UTF-8
//-- write --
//abc
//1234
//○△×

PrintWriter (Writer out)

Creates a new PrintWriter, without automatic line flushing.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(out);

// Result
// ↓
//abc
//1234
//○△×

PrintWriter (Writer out, boolean autoFlush)

Creates a new PrintWriter.

// autoFlush = false

final var sw = new StringWriter();

try (final var out = new BufferedWriter(sw);
     final var writer = new PrintWriter(out, false)) {

    writer.print("abc");
    System.out.println(sw.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.println("XYZ");
    System.out.println(sw.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.printf("num = %d", 1234);
    System.out.println(sw.toString().isEmpty());

    // Result
    // ↓
    //true
}

System.out.println(sw);

// Result
// ↓
//abcXYZ
//num = 1234
// autoFlush = true

final var sw = new StringWriter();

try (final var out = new BufferedWriter(sw);
     final var writer = new PrintWriter(out, true)) {

    writer.print("abc");
    System.out.println(sw.toString().isEmpty());

    // Result
    // ↓
    //true

    writer.println("XYZ");
    System.out.println(sw);

    // Result
    // ↓
    //abcXYZ

    writer.printf("num = %d", 1234);
    System.out.println(sw);

    // Result
    // ↓
    //abcXYZ
    //num = 1234
}

System.out.println(sw);

// Result
// ↓
//abcXYZ
//num = 1234

PrintWriter (String fileName)

Creates a new PrintWriter, without automatic line flushing, with the specified file name.

final var file = Path.of("R:", "java-work", "sample.txt");
final var fileName = file.toString();
System.out.println("file name : " + fileName);

System.out.println("-- write --");
try (final var writer = new PrintWriter(fileName)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file));

// Result
// ↓
//file name : R:\java-work\sample.txt
//-- write --
//abc
//1234
//○△×

PrintWriter (String fileName, String csn)

Creates a new PrintWriter, without automatic line flushing, with the specified file name and charset.

System.out.println("default charset : " + Charset.defaultCharset());

final var file = Path.of("R:", "java-work", "sample.txt");
final var fileName = file.toString();
System.out.println("file name : " + fileName);

final var csn = "Shift_JIS";

System.out.println("-- write --");
try (final var writer = new PrintWriter(fileName, csn)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file, Charset.forName(csn)));

// Result
// ↓
//default charset : UTF-8
//file name : R:\java-work\sample.txt
//-- write --
//abc
//1234
//○△×

PrintWriter (String fileName, Charset charset)

Creates a new PrintWriter, without automatic line flushing, with the specified file name and charset.

System.out.println("default charset : " + Charset.defaultCharset());

final var file = Path.of("R:", "java-work", "sample.txt");
final var fileName = file.toString();
System.out.println("file name : " + fileName);

final var charset = Charset.forName("Shift_JIS");

System.out.println("-- write --");
try (final var writer = new PrintWriter(fileName, charset)) {
    writer.println("abc");
    writer.println(1234);
    writer.println("○△×");
}

System.out.print(Files.readString(file, charset));

// Result
// ↓
//default charset : UTF-8
//file name : R:\java-work\sample.txt
//-- write --
//abc
//1234
//○△×

Methods

PrintWriter append (char c)

Appends the specified character to this writer.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.append('a').append('b').append('c');
}

System.out.println(out); // abc

PrintWriter append (CharSequence csq)

Appends the specified character sequence to this writer.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.append("abc").append("-").append("XYZ");
}

System.out.println(out); // abc-XYZ

PrintWriter append (CharSequence csq, int start, int end)

Appends a subsequence of the specified character sequence to this writer.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {
    final var csq = "abcd";

    writer.append(csq, 0, 1).println();
    writer.append(csq, 0, 2).println();
    writer.append(csq, 0, 3).println();
    writer.append(csq, 0, 4).println();
}

System.out.print(out);

// Result
// ↓
//a
//ab
//abc
//abcd
final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {
    final var csq = "abcd";

    writer.append(csq, 0, 4).println();
    writer.append(csq, 1, 4).println();
    writer.append(csq, 2, 4).println();
    writer.append(csq, 3, 4).println();
}

System.out.print(out);

// Result
// ↓
//abcd
//bcd
//cd
//d

boolean checkError ()

Flushes the stream if it's not closed and checks its error state.

final var file = Path.of("R:", "java-work", "sample.txt");

try (final var out = Files.newBufferedWriter(file);
     final var writer = new PrintWriter(out)) {

    writer.println("abc");

    System.out.println("error : " + writer.checkError());

    // Intentionally close the out object to make an error.
    System.out.println("-- close --");
    out.close();

    writer.println("XYZ");

    System.out.println("error : " + writer.checkError());
}

// Result
// ↓
//error : false
//-- close --
//error : true

protected void clearError ()

Clears the error state of this stream.

protected. I think it's rare to create a subclass of PrintWriter. Therefore, the code example is omitted.

void close ()

Closes the stream and releases any system resources associated with it.

final var file = Path.of("R:", "java-work", "sample.txt");

try (final var writer = new PrintWriter(file.toFile())) {
    writer.print("abc");
    writer.print("XYZ");
}

System.out.println(Files.readString(file)); // abcXYZ
// An example without a try-with-resources statement.
final var file = Path.of("R:", "java-work", "sample.txt");

final var writer = new PrintWriter(file.toFile());
try {
    writer.print("abc");
    writer.print("XYZ");
} finally {
    writer.close();
}

System.out.println(Files.readString(file)); // abcXYZ

void flush ()

Flushes the stream.

final var out = new ByteArrayOutputStream();
try (final var writer = new PrintWriter(out, false)) {

    writer.print("abc");
    System.out.println(out.toString().isEmpty()); // true

    writer.print(123);
    System.out.println(out.toString().isEmpty()); // true

    writer.flush();
    System.out.println(out); // abc123
}

PrintWriter format (String format, Object... args)

Writes a formatted string to this writer using the specified format string and arguments.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.format("text = %s%n", "abc");
    writer.format("num = %d%n", 1234);

    writer.format("X").format("Y").format("Z");
}

System.out.println(out);

// Result
// ↓
//text = abc
//num = 1234
//XYZ

PrintWriter format (Locale l, String format, Object... args)

Writes a formatted string to this writer using the specified format string and arguments.

System.out.println("locale : " + Locale.getDefault());

System.out.println("-- write --");
final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final var time = LocalTime.of(14, 30);
    writer.format("%tr%n", time);
    writer.format(Locale.JAPANESE, "%tr%n", time);
}

System.out.print(out);

// Result
// ↓
//locale : en_US
//-- write --
//02:30:00 PM
//02:30:00 午後

void print (boolean b)

Prints a boolean value.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(true);
    writer.print(" : ");
    writer.print(false);
}

System.out.println(out); // true : false

void print (char c)

Prints a character.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print('a');
    writer.print(" : ");
    writer.print('b');
}

System.out.println(out); // a : b

void print (char[] s)

Prints an array of characters.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(new char[]{'a', 'b', 'c'});
    writer.print(" : ");
    writer.print(new char[]{'X', 'Y', 'Z'});
}

System.out.println(out); // abc : XYZ

void print (double d)

Prints a double-precision floating-point number.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(1.234);
    writer.print(" : ");
    writer.print(7.89e+10);
}

System.out.println(out); // 1.234 : 7.89E10

void print (float f)

Prints a floating-point number.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(1.234f);
    writer.print(" : ");
    writer.print(7.89e+10f);
}

System.out.println(out); // 1.234 : 7.8900003E10

void print (int i)

Prints an integer.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(1234);
    writer.print(" : ");
    writer.print(Integer.MAX_VALUE);
}

System.out.println(out); // 1234 : 2147483647

void print (long l)

Prints a long integer.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(1234L);
    writer.print(" : ");
    writer.print(Long.MAX_VALUE);
}

System.out.println(out); // 1234 : 9223372036854775807

void print (Object obj)

Prints an object.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print(Path.of("R:", "java-work"));
    writer.print(" : ");
    writer.print(LocalTime.of(14, 30));
}

System.out.println(out); // R:\java-work : 14:30

void print (String s)

Prints a string.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.print("abc");
    writer.print(" : ");
    writer.print("XYZ");
}

System.out.println(out); // abc : XYZ

PrintWriter printf (String format, Object... args)

A convenience method to write a formatted string to this writer using the specified format string and arguments.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.printf("text = %s%n", "abc");
    writer.printf("num = %d%n", 1234);

    writer.printf("X").printf("Y").printf("Z");
}

System.out.println(out);

// Result
// ↓
//text = abc
//num = 1234
//XYZ

PrintWriter printf (Locale l, String format, Object... args)

A convenience method to write a formatted string to this writer using the specified format string and arguments.

System.out.println("locale : " + Locale.getDefault());

System.out.println("-- write --");
final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final var time = LocalTime.of(14, 30);
    writer.printf("%tr%n", time);
    writer.printf(Locale.JAPANESE, "%tr%n", time);
}

System.out.print(out);

// Result
// ↓
//locale : en_US
//-- write --
//02:30:00 PM
//02:30:00 午後

void println ()

Terminates the current line by writing the line separator string.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {
    writer.print("abc");
    writer.println();
    writer.print(123);
}

System.out.println(out);

// Result
// ↓
//abc
//123

void println (boolean x)

Prints a boolean value and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(true);
    writer.println(false);
}

System.out.print(out);

// Result
// ↓
//true
//false

void println (char x)

Prints a character and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println('a');
    writer.println('b');
}

System.out.print(out);

// Result
// ↓
//a
//b

void println (char[] x)

Prints an array of characters and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(new char[]{'a', 'b', 'c'});
    writer.println(new char[]{'X', 'Y', 'Z'});
}

System.out.print(out);

// Result
// ↓
//abc
//XYZ

void println (double x)

Prints a double-precision floating-point number and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(1.234);
    writer.println(7.89e+10);
}

System.out.print(out);

// Result
// ↓
//1.234
//7.89E10

void println (float x)

Prints a floating-point number and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(1.234f);
    writer.println(7.89e+10f);
}

System.out.print(out);

// Result
// ↓
//1.234
//7.8900003E10

void println (int x)

Prints an integer and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(1234);
    writer.println(Integer.MAX_VALUE);
}

System.out.print(out);

// Result
// ↓
//1234
//2147483647

void println (long x)

Prints a long integer and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(1234L);
    writer.println(Long.MAX_VALUE);
}

System.out.print(out);

// Result
// ↓
//1234
//9223372036854775807

void println (Object x)

Prints an Object and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println(Path.of("R:", "java-work"));
    writer.println(LocalTime.of(14, 30));
}

System.out.print(out);

// Result
// ↓
//R:\java-work
//14:30

void println (String x)

Prints a String and then terminates the line.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.println("abc");
    writer.println("XYZ");
}

System.out.print(out);

// Result
// ↓
//abc
//XYZ

protected void setError ()

Indicates that an error has occurred.

protected. I think it's rare to create a subclass of PrintWriter. Therefore, the code example is omitted.

void write (char[] buf)

Writes an array of characters.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.write(new char[]{'a', 'b', 'c'});
    writer.write(new char[]{'X', 'Y', 'Z'});
}

System.out.println(out); // abcXYZ

void write (char[] buf, int off, int len)

Writes A Portion of an array of characters.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final char[] buf = {'a', 'b', 'c', 'd'};

    writer.write(buf, 0, 1);
    writer.println();

    writer.write(buf, 0, 2);
    writer.println();

    writer.write(buf, 0, 3);
    writer.println();

    writer.write(buf, 0, 4);
    writer.println();
}

System.out.print(out);

// Result
// ↓
//a
//ab
//abc
//abcd
final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final char[] buf = {'a', 'b', 'c', 'd'};

    writer.write(buf, 0, 4);
    writer.println();

    writer.write(buf, 1, 3);
    writer.println();

    writer.write(buf, 2, 2);
    writer.println();

    writer.write(buf, 3, 1);
    writer.println();
}

System.out.print(out);

// Result
// ↓
//abcd
//bcd
//cd
//d

void write (int c)

Writes a single character.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.write('a');
    writer.write('b');
    writer.write('c');
}

System.out.println(out); // abc

void write (String s)

Writes a string.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    writer.write("abc");
    writer.write("XYZ");
}

System.out.println(out); // abcXYZ

void write (String s, int off, int len)

Writes a portion of a string.

final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final var s = "abcd";

    writer.write(s, 0, 1);
    writer.println();

    writer.write(s, 0, 2);
    writer.println();

    writer.write(s, 0, 3);
    writer.println();

    writer.write(s, 0, 4);
    writer.println();
}

System.out.print(out);

// Result
// ↓
//a
//ab
//abc
//abcd
final var out = new StringWriter();
try (final var writer = new PrintWriter(out)) {

    final var s = "abcd";

    writer.write(s, 0, 4);
    writer.println();

    writer.write(s, 1, 3);
    writer.println();

    writer.write(s, 2, 2);
    writer.println();

    writer.write(s, 3, 1);
    writer.println();
}

System.out.print(out);

// Result
// ↓
//abcd
//bcd
//cd
//d

Methods declared in Writer

nullWriter

Please see the link below.


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