StringBuffer

class StringBuffer implements StringSink

A class for concatenating strings efficiently.

Allows for the incremental building of a string using write*() methods. The strings are concatenated to a single string only when toString is called.

Example:

final buffer = StringBuffer('DART');
print(buffer.length); // 4

To add the string representation of an object, as returned by Object.toString, to the buffer, use write. Is also used for adding a string directly.

buffer.write(' is open source');
print(buffer.length); // 19
print(buffer); // DART is open source

const int dartYear = 2011;
buffer
  ..write(' since ') // Writes a string.
  ..write(dartYear); // Writes an int.
print(buffer); // DART is open source since 2011
print(buffer.length); // 30

To add a newline after the object's string representation, use writeln. Calling writeln with no argument adds a single newline to the buffer.

buffer.writeln(); // Contains "DART is open source since 2011\n".
buffer.writeln('-' * (buffer.length - 1)); // 30 '-'s and a newline.
print(buffer.length); // 62

To write multiple objects to the buffer, use writeAll.

const separator = '-';
buffer.writeAll(['Dart', 'is', 'fun!'], separator);
print(buffer.length); // 74
print(buffer);
// DART is open source since 2011
// ------------------------------
// Dart-is-fun!

To add the string representation of a Unicode code point, charCode, to the buffer, use writeCharCode.

buffer.writeCharCode(0x0A); // LF (line feed)
buffer.writeCharCode(0x44); // 'D'
buffer.writeCharCode(0x61); // 'a'
buffer.writeCharCode(0x72); // 'r'
buffer.writeCharCode(0x74); // 't'
print(buffer.length); // 79

To convert the content to a single string, use toString.

final text = buffer.toString();
print(text);
// DART is open source since 2011
// ------------------------------
// Dart-is-fun!
// Dart

To clear the buffer, so that it can be reused, use clear.

buffer.clear();
print(buffer.isEmpty); // true
print(buffer.length); // 0

Implemented types

• StringSink

Constructors

StringBuffer()

StringBuffer([Object content = ""])

Creates a string buffer containing the provided content.

Implementation

external StringBuffer([Object content = ""]);

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

isEmpty no setter

bool get isEmpty

Returns whether the buffer is empty. This is a constant-time operation.

Implementation

bool get isEmpty => length == 0;

isNotEmpty no setter

bool get isNotEmpty

Returns whether the buffer is not empty. This is a constant-time operation.

Implementation

bool get isNotEmpty => !isEmpty;

length no setter

int get length

Returns the length of the content that has been accumulated so far. This is a constant-time operation.

Implementation

external int get length;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

clear()

void clear()

Clears the string buffer.

Implementation

external void clear();

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() override

String toString()

Returns the contents of buffer as a single string.

Implementation

external String toString();

write() override

void write(Object? object)

Writes the string representation of object.

Converts object to a string using object.toString().

Notice that calling sink.write(null) will will write the "null" string.

Implementation

external void write(Object? object);

writeAll() override

void writeAll(Iterable<dynamic> objects, [String separator = ""])

Writes the elements of objects separated by separator.

Writes the string representation of every element of objects, in iteration order, and writes separator between any two elements.

sink.writeAll(["Hello", "World"], " Beautiful ");

is equivalent to:

sink
  ..write("Hello");
  ..write(" Beautiful ");
  ..write("World");

Implementation

external void writeAll(Iterable<dynamic> objects, [String separator = ""]);

writeCharCode() override

void writeCharCode(int charCode)

Writes a string containing the character with code point charCode.

Equivalent to write(String.fromCharCode(charCode)).

Implementation

external void writeCharCode(int charCode);

writeln() override

void writeln([Object? obj = ""])

Writes the string representation of object followed by a newline.

Equivalent to buffer.write(object) followed by buffer.write("\n").

The newline is always represented as "\n", and does not use a platform specific line ending, e.g., "\r\n" on Windows.

Notice that calling buffer.writeln(null) will write the "null" string before the newline. Omitting the argument, or explicitly passing an empty string, is the recommended way to emit just the newline.

Implementation

external void writeln([Object? obj = ""]);

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);