Interactive Programming In Java

Selected String Methods

Below are some selected methods that can be invoked on individual Strings, along with brief explanations and examples of their usage.

toUpperCase toLowerCase trim substring length replace charAt indexOf lastIndexOf

toUpperCase() produces a String just like the String you start with, but in which all letters are capitalized. For example,
    "MixedCaseString".toUpperCase()
produces
    "MIXEDCASESTRING"

toLowerCase() produces a similar String in which all letters are in lower case. So
    "MixedCaseString".toLowerCase()
produces
    "mixedcasestring"

trim() produces a similar String in which all leading and trailing white space (spaces, tabs, etc.) has been removed. So
    "    a very spacey String    ".trim()
is just
    "a very spacey String"

substring( fromIndex) produces a shorter String containing the same characters that you started with, but beginning at index fromIndex. Bear in mind that the index of the first character of a String is 0.

substring( fromIndex,toIndex ) produces the substring that begins at index fromIndex and ends at toIndex - 1.
    "Hello".substring(3) is "lo"
    "Hello".substring(1, 4) is "ell", and
    "Hello".substring(0) is "Hello" again.

length() returns the number of characters in the String. For example,
    "Tee hee!".length()
is 8. Since the String is indexed starting at 0, the index of the final character in the String is the String's length() - 1.

replace( old,new ) requires two characters, old and new, and produces a new String in which each occurrence of old is replaced by new: [Footnote: A character is, roughly, a single alphanumeric or symbolic character (one keystroke) inside single quotation marks. For more detail on what exactly constitutes a character, see the chapter on Java types.] For example,
    "Tee hee!".replace('e', '*')
produces
    "T** h**!"

charAt( pos ) requires an index into the String and returns the character at that index. Recall that Strings are indexed starting at 0.
    "Hello".charAt(2) returns the same character as "Hello".charAt(3)

indexOf( character) returns the lowest number that is an index of character in the String.
    "Hello".indexOf('H') is 0 and
    "Hello".indexOf('l') is 2. Also,
    "Hello".indexOf('x') is -1, indicating that 'x' does not appear in "Hello".

lastIndexOf( character) returns the highest number that is an index of character in the String.
    "Hello".lastIndexOf('H') is 0 and
    "Hello".lastIndexOf('x') is -1, but
    "Hello".lastIndexOf('l') is 3.