Package java.lang

Class StringBuilder

java.lang.Object
java.lang.StringBuilder
All Implemented Interfaces:
Serializable, Appendable, CharSequence
public final class StringBuilder
extends Object
implements Appendable, CharSequence, Serializable
A modifiable sequence of characters for use in creating strings. This class is intended as a direct replacement of StringBuffer for non-concurrent use; unlike StringBuffer this class is not synchronized.

For particularly complex string-building needs, consider Formatter.

The majority of the modification methods on this class return this so that method calls can be chained together. For example: new StringBuilder("a").append("b").append("c").toString().

Since:
1.5
See Also:
CharSequence, Appendable, StringBuffer, String, String.format(java.lang.String, java.lang.Object...), Serialized Form

  • Constructor Summary

    Constructors
    Constructor Description
    StringBuilder()
    Constructs an instance with an initial capacity of 16.
    StringBuilder​(int capacity)
    Constructs an instance with the specified capacity.
    StringBuilder​(CharSequence seq)
    Constructs an instance that's initialized with the contents of the specified CharSequence.
    StringBuilder​(String str)
    Constructs an instance that's initialized with the contents of the specified String.

  • Method Summary

    Modifier and Type Method Description
    StringBuilder append​(boolean b)
    Appends the string representation of the specified boolean value.
    StringBuilder append​(char c)
    Appends the string representation of the specified char value.
    StringBuilder append​(char[] chars)
    Appends the string representation of the specified char[].
    StringBuilder append​(char[] str, int offset, int len)
    Appends the string representation of the specified subset of the char[].
    StringBuilder append​(double d)
    Appends the string representation of the specified double value.
    StringBuilder append​(float f)
    Appends the string representation of the specified float value.
    StringBuilder append​(int i)
    Appends the string representation of the specified int value.
    StringBuilder append​(long l)
    Appends the string representation of the specified long value.
    StringBuilder append​(CharSequence csq)
    Appends the string representation of the specified CharSequence.
    StringBuilder append​(CharSequence csq, int start, int end)
    Appends the string representation of the specified subsequence of the CharSequence.
    StringBuilder append​(Object obj)
    Appends the string representation of the specified Object.
    StringBuilder append​(String str)
    Appends the contents of the specified string.
    StringBuilder append​(StringBuffer sb)
    Appends the contents of the specified StringBuffer.
    StringBuilder appendCodePoint​(int codePoint)
    Appends the encoded Unicode code point.
    int capacity()
    Returns the number of characters that can be held without growing.
    char charAt​(int index)
    Retrieves the character at the index.
    int codePointAt​(int index)
    Retrieves the Unicode code point value at the index.
    int codePointBefore​(int index)
    Retrieves the Unicode code point value that precedes the index.
    int codePointCount​(int start, int end)
    Calculates the number of Unicode code points between start and end.
    StringBuilder delete​(int start, int end)
    Deletes a sequence of characters specified by start and end.
    StringBuilder deleteCharAt​(int index)
    Deletes the character at the specified index.
    void ensureCapacity​(int min)
    Ensures that this object has a minimum capacity available before requiring the internal buffer to be enlarged.
    void getChars​(int start, int end, char[] dst, int dstStart)
    Copies the requested sequence of characters into dst passed starting at dst.
    int indexOf​(String string)
    Searches for the first index of the specified character.
    int indexOf​(String subString, int start)
    Searches for the index of the specified character.
    StringBuilder insert​(int offset, boolean b)
    Inserts the string representation of the specified boolean value at the specified offset.
    StringBuilder insert​(int offset, char c)
    Inserts the string representation of the specified char value at the specified offset.
    StringBuilder insert​(int offset, char[] ch)
    Inserts the string representation of the specified char[] at the specified offset.
    StringBuilder insert​(int offset, char[] str, int strOffset, int strLen)
    Inserts the string representation of the specified subsequence of the char[] at the specified offset.
    StringBuilder insert​(int offset, double d)
    Inserts the string representation of the specified double value at the specified offset.
    StringBuilder insert​(int offset, float f)
    Inserts the string representation of the specified float value at the specified offset.
    StringBuilder insert​(int offset, int i)
    Inserts the string representation of the specified int value at the specified offset.
    StringBuilder insert​(int offset, long l)
    Inserts the string representation of the specified long value at the specified offset.
    StringBuilder insert​(int offset, CharSequence s)
    Inserts the string representation of the specified CharSequence at the specified offset.
    StringBuilder insert​(int offset, CharSequence s, int start, int end)
    Inserts the string representation of the specified subsequence of the CharSequence at the specified offset.
    StringBuilder insert​(int offset, Object obj)
    Inserts the string representation of the specified Object at the specified offset.
    StringBuilder insert​(int offset, String str)
    Inserts the specified string at the specified offset.
    int lastIndexOf​(String string)
    Searches for the last index of the specified character.
    int lastIndexOf​(String subString, int start)
    Searches for the index of the specified character.
    int length()
    The current length.
    int offsetByCodePoints​(int index, int codePointOffset)
    Returns the index that is offset codePointOffset code points from index.
    StringBuilder replace​(int start, int end, String string)
    Replaces the specified subsequence in this builder with the specified string.
    StringBuilder reverse()
    Reverses the order of characters in this builder.
    void setCharAt​(int index, char ch)
    Sets the character at the index.
    void setLength​(int length)
    Sets the current length to a new value.
    CharSequence subSequence​(int start, int end)
    Returns a CharSequence of the subsequence from the start index to the end index.
    String substring​(int start)
    Returns the String value of the subsequence from the start index to the current end.
    String substring​(int start, int end)
    Returns the String value of the subsequence from the start index to the end index.
    String toString()
    Returns the contents of this builder.
    void trimToSize()
    Trims off any extra capacity beyond the current length.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods inherited from interface java.lang.CharSequence

    charAt, length, subSequence

  • Constructor Details

    • StringBuilder

      public StringBuilder()
      Constructs an instance with an initial capacity of 16.
      See Also:
      capacity()

    • StringBuilder

      public StringBuilder​(int capacity)
      Constructs an instance with the specified capacity.
      Parameters:
      capacity - the initial capacity to use.
      Throws:
      NegativeArraySizeException - if the specified capacity is negative.
      See Also:
      capacity()

    • StringBuilder

      public StringBuilder​(CharSequence seq)
      Constructs an instance that's initialized with the contents of the specified CharSequence. The capacity of the new builder will be the length of the CharSequence plus 16.
      Parameters:
      seq - the CharSequence to copy into the builder.
      Throws:
      NullPointerException - if seq is null.

    • StringBuilder

      public StringBuilder​(String str)
      Constructs an instance that's initialized with the contents of the specified String. The capacity of the new builder will be the length of the String plus 16.
      Parameters:
      str - the String to copy into the builder.
      Throws:
      NullPointerException - if str is null.

  • Method Details

    • append

      public StringBuilder append​(boolean b)
      Appends the string representation of the specified boolean value. The boolean value is converted to a String according to the rule defined by String.valueOf(boolean).
      Parameters:
      b - the boolean value to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(boolean)

    • append

      public StringBuilder append​(char c)
      Appends the string representation of the specified char value. The char value is converted to a string according to the rule defined by String.valueOf(char).
      Specified by:
      append in interface Appendable
      Parameters:
      c - the char value to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(char)

    • append

      public StringBuilder append​(int i)
      Appends the string representation of the specified int value. The int value is converted to a string according to the rule defined by String.valueOf(int).
      Parameters:
      i - the int value to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(int)

    • append

      public StringBuilder append​(long l)
      Appends the string representation of the specified long value. The long value is converted to a string according to the rule defined by String.valueOf(long).
      Parameters:
      l - the long value.
      Returns:
      this builder.
      See Also:
      String.valueOf(long)

    • append

      public StringBuilder append​(float f)
      Appends the string representation of the specified float value. The float value is converted to a string according to the rule defined by String.valueOf(float).
      Parameters:
      f - the float value to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(float)

    • append

      public StringBuilder append​(double d)
      Appends the string representation of the specified double value. The double value is converted to a string according to the rule defined by String.valueOf(double).
      Parameters:
      d - the double value to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(double)

    • append

      public StringBuilder append​(Object obj)
      Appends the string representation of the specified Object. The Object value is converted to a string according to the rule defined by String.valueOf(Object).
      Parameters:
      obj - the Object to append.
      Returns:
      this builder.
      See Also:
      String.valueOf(Object)

    • append

      public StringBuilder append​(String str)
      Appends the contents of the specified string. If the string is null, then the string "null" is appended.
      Parameters:
      str - the string to append.
      Returns:
      this builder.

    • append

      public StringBuilder append​(StringBuffer sb)
      Appends the contents of the specified StringBuffer. If the StringBuffer is null, then the string "null" is appended.
      Parameters:
      sb - the StringBuffer to append.
      Returns:
      this builder.

    • append

      public StringBuilder append​(char[] chars)
      Appends the string representation of the specified char[]. The char[] is converted to a string according to the rule defined by String.valueOf(char[]).
      Parameters:
      chars - the char[] to append..
      Returns:
      this builder.
      See Also:
      String.valueOf(char[])

    • append

      public StringBuilder append​(char[] str, int offset, int len)
      Appends the string representation of the specified subset of the char[]. The char[] value is converted to a String according to the rule defined by String.valueOf(char[],int,int).
      Parameters:
      str - the char[] to append.
      offset - the inclusive offset index.
      len - the number of characters.
      Returns:
      this builder.
      Throws:
      ArrayIndexOutOfBoundsException - if offset and len do not specify a valid subsequence.
      See Also:
      String.valueOf(char[],int,int)

    • append

      public StringBuilder append​(CharSequence csq)
      Appends the string representation of the specified CharSequence. If the CharSequence is null, then the string "null" is appended.
      Specified by:
      append in interface Appendable
      Parameters:
      csq - the CharSequence to append.
      Returns:
      this builder.

    • append

      public StringBuilder append​(CharSequence csq, int start, int end)
      Appends the string representation of the specified subsequence of the CharSequence. If the CharSequence is null, then the string "null" is used to extract the subsequence from.
      Specified by:
      append in interface Appendable
      Parameters:
      csq - the CharSequence to append.
      start - the beginning index.
      end - the ending index.
      Returns:
      this builder.
      Throws:
      IndexOutOfBoundsException - if start or end are negative, start is greater than end or end is greater than the length of csq.

    • appendCodePoint

      public StringBuilder appendCodePoint​(int codePoint)
      Appends the encoded Unicode code point. The code point is converted to a char[] as defined by Character.toChars(int).
      Parameters:
      codePoint - the Unicode code point to encode and append.
      Returns:
      this builder.
      See Also:
      Character.toChars(int)

    • delete

      public StringBuilder delete​(int start, int end)
      Deletes a sequence of characters specified by start and end. Shifts any remaining characters to the left.
      Parameters:
      start - the inclusive start index.
      end - the exclusive end index.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if start is less than zero, greater than the current length or greater than end.

    • deleteCharAt

      public StringBuilder deleteCharAt​(int index)
      Deletes the character at the specified index. shifts any remaining characters to the left.
      Parameters:
      index - the index of the character to delete.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if index is less than zero or is greater than or equal to the current length.

    • insert

      public StringBuilder insert​(int offset, boolean b)
      Inserts the string representation of the specified boolean value at the specified offset. The boolean value is converted to a string according to the rule defined by String.valueOf(boolean).
      Parameters:
      offset - the index to insert at.
      b - the boolean value to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length.
      See Also:
      String.valueOf(boolean)

    • insert

      public StringBuilder insert​(int offset, char c)
      Inserts the string representation of the specified char value at the specified offset. The char value is converted to a string according to the rule defined by String.valueOf(char).
      Parameters:
      offset - the index to insert at.
      c - the char value to insert.
      Returns:
      this builder.
      Throws:
      IndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(char)

    • insert

      public StringBuilder insert​(int offset, int i)
      Inserts the string representation of the specified int value at the specified offset. The int value is converted to a String according to the rule defined by String.valueOf(int).
      Parameters:
      offset - the index to insert at.
      i - the int value to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(int)

    • insert

      public StringBuilder insert​(int offset, long l)
      Inserts the string representation of the specified long value at the specified offset. The long value is converted to a String according to the rule defined by String.valueOf(long).
      Parameters:
      offset - the index to insert at.
      l - the long value to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current {code length()}.
      See Also:
      String.valueOf(long)

    • insert

      public StringBuilder insert​(int offset, float f)
      Inserts the string representation of the specified float value at the specified offset. The float value is converted to a string according to the rule defined by String.valueOf(float).
      Parameters:
      offset - the index to insert at.
      f - the float value to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(float)

    • insert

      public StringBuilder insert​(int offset, double d)
      Inserts the string representation of the specified double value at the specified offset. The double value is converted to a String according to the rule defined by String.valueOf(double).
      Parameters:
      offset - the index to insert at.
      d - the double value to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(double)

    • insert

      public StringBuilder insert​(int offset, Object obj)
      Inserts the string representation of the specified Object at the specified offset. The Object value is converted to a String according to the rule defined by String.valueOf(Object).
      Parameters:
      offset - the index to insert at.
      obj - the Object to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(Object)

    • insert

      public StringBuilder insert​(int offset, String str)
      Inserts the specified string at the specified offset. If the specified string is null, then the String "null" is inserted.
      Parameters:
      offset - the index to insert at.
      str - the String to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().

    • insert

      public StringBuilder insert​(int offset, char[] ch)
      Inserts the string representation of the specified char[] at the specified offset. The char[] value is converted to a String according to the rule defined by String.valueOf(char[]).
      Parameters:
      offset - the index to insert at.
      ch - the char[] to insert.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      String.valueOf(char[])

    • insert

      public StringBuilder insert​(int offset, char[] str, int strOffset, int strLen)
      Inserts the string representation of the specified subsequence of the char[] at the specified offset. The char[] value is converted to a String according to the rule defined by String.valueOf(char[],int,int).
      Parameters:
      offset - the index to insert at.
      str - the char[] to insert.
      strOffset - the inclusive index.
      strLen - the number of characters.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if offset is negative or greater than the current length(), or strOffset and strLen do not specify a valid subsequence.
      See Also:
      String.valueOf(char[],int,int)

    • insert

      public StringBuilder insert​(int offset, CharSequence s)
      Inserts the string representation of the specified CharSequence at the specified offset. The CharSequence is converted to a String as defined by CharSequence.toString(). If s is null, then the String "null" is inserted.
      Parameters:
      offset - the index to insert at.
      s - the CharSequence to insert.
      Returns:
      this builder.
      Throws:
      IndexOutOfBoundsException - if offset is negative or greater than the current length().
      See Also:
      CharSequence.toString()

    • insert

      public StringBuilder insert​(int offset, CharSequence s, int start, int end)
      Inserts the string representation of the specified subsequence of the CharSequence at the specified offset. The CharSequence is converted to a String as defined by CharSequence.subSequence(int, int). If the CharSequence is null, then the string "null" is used to determine the subsequence.
      Parameters:
      offset - the index to insert at.
      s - the CharSequence to insert.
      start - the start of the subsequence of the character sequence.
      end - the end of the subsequence of the character sequence.
      Returns:
      this builder.
      Throws:
      IndexOutOfBoundsException - if offset is negative or greater than the current length(), or start and end do not specify a valid subsequence.
      See Also:
      CharSequence.subSequence(int, int)

    • replace

      public StringBuilder replace​(int start, int end, String string)
      Replaces the specified subsequence in this builder with the specified string.
      Parameters:
      start - the inclusive begin index.
      end - the exclusive end index.
      string - the replacement string.
      Returns:
      this builder.
      Throws:
      StringIndexOutOfBoundsException - if start is negative, greater than the current length() or greater than end.
      NullPointerException - if str is null.

    • reverse

      public StringBuilder reverse()
      Reverses the order of characters in this builder.
      Returns:
      this buffer.

    • toString

      public String toString()
      Returns the contents of this builder.
      Specified by:
      toString in interface CharSequence
      Returns:
      the string representation of the data in this builder.

    • capacity

      public int capacity()
      Returns the number of characters that can be held without growing.
      Returns:
      the capacity
      See Also:
      ensureCapacity(int), length()

    • charAt

      public char charAt​(int index)
      Retrieves the character at the index.
      Parameters:
      index - the index of the character to retrieve.
      Returns:
      the char value.
      Throws:
      IndexOutOfBoundsException - if index is negative or greater than or equal to the current length().

    • ensureCapacity

      public void ensureCapacity​(int min)
      Ensures that this object has a minimum capacity available before requiring the internal buffer to be enlarged. The general policy of this method is that if the minimumCapacity is larger than the current capacity(), then the capacity will be increased to the largest value of either the minimumCapacity or the current capacity multiplied by two plus two. Although this is the general policy, there is no guarantee that the capacity will change.
      Parameters:
      min - the new minimum capacity to set.

    • getChars

      public void getChars​(int start, int end, char[] dst, int dstStart)
      Copies the requested sequence of characters into dst passed starting at dst.
      Parameters:
      start - the inclusive start index of the characters to copy.
      end - the exclusive end index of the characters to copy.
      dst - the char[] to copy the characters to.
      dstStart - the inclusive start index of dst to begin copying to.
      Throws:
      IndexOutOfBoundsException - if the start is negative, the dstStart is negative, the start is greater than end, the end is greater than the current length() or dstStart + end - begin is greater than dst.length.

    • length

      public int length()
      The current length.
      Returns:
      the number of characters contained in this instance.

    • setCharAt

      public void setCharAt​(int index, char ch)
      Sets the character at the index.
      Parameters:
      index - the zero-based index of the character to replace.
      ch - the character to set.
      Throws:
      IndexOutOfBoundsException - if index is negative or greater than or equal to the current length().

    • setLength

      public void setLength​(int length)
      Sets the current length to a new value. If the new length is larger than the current length, then the new characters at the end of this object will contain the char value of .
      Parameters:
      length - the new length of this StringBuffer.
      Throws:
      IndexOutOfBoundsException - if length < 0.
      See Also:
      length()

    • substring

      public String substring​(int start)
      Returns the String value of the subsequence from the start index to the current end.
      Parameters:
      start - the inclusive start index to begin the subsequence.
      Returns:
      a String containing the subsequence.
      Throws:
      StringIndexOutOfBoundsException - if start is negative or greater than the current length().

    • substring

      public String substring​(int start, int end)
      Returns the String value of the subsequence from the start index to the end index.
      Parameters:
      start - the inclusive start index to begin the subsequence.
      end - the exclusive end index to end the subsequence.
      Returns:
      a String containing the subsequence.
      Throws:
      StringIndexOutOfBoundsException - if start is negative, greater than end or if end is greater than the current length().

    • subSequence

      public CharSequence subSequence​(int start, int end)
      Returns a CharSequence of the subsequence from the start index to the end index.
      Parameters:
      start - the inclusive start index to begin the subsequence.
      end - the exclusive end index to end the subsequence.
      Returns:
      a CharSequence containing the subsequence.
      Throws:
      IndexOutOfBoundsException - if start is negative, greater than end or if end is greater than the current length().
      Since:
      1.4

    • indexOf

      public int indexOf​(String string)
      Searches for the first index of the specified character. The search for the character starts at the beginning and moves towards the end.
      Parameters:
      string - the string to find.
      Returns:
      the index of the specified character, -1 if the character isn't found.
      Since:
      1.4
      See Also:
      lastIndexOf(String)

    • indexOf

      public int indexOf​(String subString, int start)
      Searches for the index of the specified character. The search for the character starts at the specified offset and moves towards the end.
      Parameters:
      subString - the string to find.
      start - the starting offset.
      Returns:
      the index of the specified character, -1 if the character isn't found
      Since:
      1.4
      See Also:
      lastIndexOf(String,int)

    • lastIndexOf

      public int lastIndexOf​(String string)
      Searches for the last index of the specified character. The search for the character starts at the end and moves towards the beginning.
      Parameters:
      string - the string to find.
      Returns:
      the index of the specified character, -1 if the character isn't found.
      Throws:
      NullPointerException - if string is null.
      Since:
      1.4
      See Also:
      String.lastIndexOf(java.lang.String)

    • lastIndexOf

      public int lastIndexOf​(String subString, int start)
      Searches for the index of the specified character. The search for the character starts at the specified offset and moves towards the beginning.
      Parameters:
      subString - the string to find.
      start - the starting offset.
      Returns:
      the index of the specified character, -1 if the character isn't found.
      Throws:
      NullPointerException - if subString is null.
      Since:
      1.4
      See Also:
      String.lastIndexOf(String,int)

    • trimToSize

      public void trimToSize()
      Trims off any extra capacity beyond the current length. Note, this method is NOT guaranteed to change the capacity of this object.
      Since:
      1.5

    • codePointAt

      public int codePointAt​(int index)
      Retrieves the Unicode code point value at the index.
      Parameters:
      index - the index to the char code unit.
      Returns:
      the Unicode code point value.
      Throws:
      IndexOutOfBoundsException - if index is negative or greater than or equal to length().
      Since:
      1.5
      See Also:
      Character, Character.codePointAt(char[], int, int)

    • codePointBefore

      public int codePointBefore​(int index)
      Retrieves the Unicode code point value that precedes the index.
      Parameters:
      index - the index to the char code unit within this object.
      Returns:
      the Unicode code point value.
      Throws:
      IndexOutOfBoundsException - if index is less than 1 or greater than length().
      Since:
      1.5
      See Also:
      Character, Character.codePointBefore(char[], int, int)

    • codePointCount

      public int codePointCount​(int start, int end)
      Calculates the number of Unicode code points between start and end.
      Parameters:
      start - the inclusive beginning index of the subsequence.
      end - the exclusive end index of the subsequence.
      Returns:
      the number of Unicode code points in the subsequence.
      Throws:
      IndexOutOfBoundsException - if start is negative or greater than end or end is greater than length().
      Since:
      1.5
      See Also:
      Character, Character.codePointCount(char[], int, int)

    • offsetByCodePoints

      public int offsetByCodePoints​(int index, int codePointOffset)
      Returns the index that is offset codePointOffset code points from index.
      Parameters:
      index - the index to calculate the offset from.
      codePointOffset - the number of code points to count.
      Returns:
      the index that is codePointOffset code points away from index.
      Throws:
      IndexOutOfBoundsException - if index is negative or greater than length() or if there aren't enough code points before or after index to match codePointOffset.
      Since:
      1.5
      See Also:
      Character, Character.offsetByCodePoints(char[], int, int, int, int)