A String literal is a sequence of zero or more characters enclosed within double quotation marks. A String object is a sequence of zero or more characters, plus a variety of class and instance methods and variables.
A String object is created automatically by Java the first time it encounters a literal string, such as "Socrates", in a program. Subsequent occurrences of the literal do not cause additional objects to be instantiated. Instead, every occurrence of the literal "Socrates" refers to the initial object.
A String object is created whenever the new operator is used in conjunction with a String() constructorfor example, new String("hello").
The String concatenation operator is the overloaded + symbol; it is used to combine two Strings into a single String: "hello" + "world" ==> "helloworld".
Strings are indexed starting at 0. The indexOf() and lastIndexOf() methods are used for finding the first or last occurrence of a character or substring within a String. The valueOf() methods convert a nonstring into a String. The length() method determines the number of characters in a String. The charAt() method returns the single character at a particular index position. The various substring() methods return the substring at particular index positions in a String.
The overloaded equals() method returns true if two Strings contain the same exact sequence of characters. The == operator, when used on Strings, returns true if two references designate the same String object.
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String objects are immutable. They cannot be modified.
A StringBuffer is a string object that can be modified using methods such as insert() and append().
A StringTokenizer is an object that can be used to break a String into a collection of tokens separated by delimiters. The white space characterstabs, blanks, and new linesare the default delimiters.
The FontMetrics class is used to obtain the specific dimensions of the various Fonts. It is useful when you wish to center text. Fonts are inherently platform dependent. For maximum portability, it is best to use default fonts.
