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The String and
StringBuffer classes
Here is an overview of the methods available for both String and StringBuffer so you can get a feel for the way they interact. These tables don’t contain every single method, but rather the ones that are important to this discussion. Methods that are overloaded are summarized in a single row.
First, the String class:
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Method
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Arguments, Overloading
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Use
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Constructor
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Overloaded: default, String, StringBuffer, char arrays, byte arrays.
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Creating String objects.
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length( )
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Number of characters in the String.
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charAt( )
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int Index
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The char at a location in the String.
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getChars( ), getBytes( )
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The beginning and end from which to copy, the array to copy into, an index into the destination array.
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Copy chars or bytes into an external array.
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toCharArray( )
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Produces a char[] containing the characters in the String.
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equals( ), equals-IgnoreCase( )
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A String to compare with.
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An equality check on the contents of the two Strings.
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compareTo( )
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A String to compare with.
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Result is negative, zero, or positive depending on the lexicographical ordering of the String and the argument. Uppercase and lowercase are not equal!
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regionMatches( )
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Offset into this String, the other String and its offset and length to compare. Overload adds “ignore case.”
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boolean result indicates whether the region matches.
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startsWith( )
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String that it might start with. Overload adds offset into argument.
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boolean result indicates whether the String starts with the argument.
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endsWith( )
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String that might be a suffix of this String.
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boolean result indicates whether the argument is a suffix.
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indexOf( ), lastIndexOf( )
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Overloaded: char, char and starting index, String, String, and starting index.
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Returns -1 if the argument is not found within this String, otherwise returns the index where the argument starts. lastIndexOf( ) searches backward from end.
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substring( )
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Overloaded: starting index, starting index, and ending index.
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Returns a new String object containing the specified character set.
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concat( )
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The String to concatenate.
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Returns a new String object containing the original String’s characters followed by the characters in the argument.
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replace( )
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The old character to search for, the new character to replace it with.
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Returns a new String object with the replacements made. Uses the old String if no match is found.
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toLowerCase( ) toUpperCase( )
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Returns a new String object with the case of all letters changed. Uses the old String if no changes need to be made.
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trim( )
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Returns a new String object with the white space removed from each end. Uses the old String if no changes need to be made.
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valueOf( )
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Overloaded: Object, char[], char[] and offset and count, boolean, char, int, long, float, double.
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Returns a String containing a character representation of the argument.
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intern( )
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Produces one and only one String reference per unique character sequence.
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You can see that every String method carefully returns a new String object when it’s necessary to change the contents. Also notice that if the contents don’t need changing, the method will just return a reference to the original String. This saves storage and overhead.
Here’s the StringBuffer class:
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Method
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Arguments, overloading
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Use
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Constructor
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Overloaded: default, length of buffer to create, String to create from.
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Create a new StringBuffer object.
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toString( )
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Creates a String from this StringBuffer.
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length( )
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Number of characters in the StringBuffer.
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capacity( )
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Returns current number of spaces allocated.
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ensure-
Capacity( )
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Integer indicating desired capacity.
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Makes the StringBuffer hold at least the desired number of spaces.
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setLength( )
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Integer indicating new length of character string in buffer.
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Truncates or expands the previous character string. If expanding, pads with nulls.
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charAt( )
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Integer indicating the location of the desired element.
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Returns the char at that location in the buffer.
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setCharAt( )
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Integer indicating the location of the desired element and the new char value for the element.
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Modifies the value at that location.
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getChars( )
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The beginning and end from which to copy, the array to copy into, an index into the destination array.
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Copy chars into an external array. There is no getBytes( ) as in String.
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append( )
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Overloaded: Object, String, char[], char[] with offset and length, boolean, char, int, long, float, double.
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The argument is converted to a string and appended to the end of the current buffer, increasing the buffer if necessary.
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insert( )
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Overloaded, each with a first argument of the offset at which to start inserting: Object, String, char[], boolean, char, int, long, float, double.
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The second argument is converted to a string and inserted into the current buffer beginning at the offset. The buffer is increased if necessary.
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reverse( )
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The order of the characters in the buffer is reversed.
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The most commonly used method is append( ), which is used by the compiler when evaluating String expressions that contain the ‘+’ and ‘+=’ operators. The insert( ) method has a similar form, and both methods perform significant manipulations to the buffer instead of creating new objects.
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