Strings Etc Part I Strings About Strings There

Strings, Etc. Part I: Strings

About Strings • There is a special syntax for constructing strings: "Hello" • Strings, unlike most other objects, have a defined operation (as opposed to a method): " This " + "is String " + "concatenation"

Useful String methods I • char. At(int index) – Returns the character at the given index position (0 based) • boolean starts. With(String prefix) – Tests if this String starts with the prefix String • boolean ends. With(String suffix) – Tests if this String ends with the suffix String

Useful String methods II • boolean equals(Object obj) – Tests if this String is the same as the obj (which may be any type; false if it’s not a String) • boolean equals. Ignore. Case(String other) – Tests if this String is equal to the other String, where case does not matter • int length() – Returns the length of this string – This is a method, not an instance variable

Useful String methods III • int index. Of(char ch) – Returns the position of the first occurrence of ch in this String, or -1 if it does not occur • int index. Of(char ch, int from. Index) – Returns the position of the first occurrence of ch, starting at (not after) the position from. Index • There are corresponding methods that take a String instead of a char as their first argument – int index. Of(String s) – int index. Of(String s, int from. Index)

Useful String methods IV • int last. Index. Of(char ch) – Returns the position of the last occurrence of ch in this String, or -1 if it does not occur • int last. Index. Of(char ch, int from. Index) – Returns the position of the last occurrence of ch, searching backward starting at position from. Index • There are corresponding methods that take a String instead of a char as their first argument

Useful String methods V • String substring(int begin. Index) – Returns a new string that is a substring of this string, starting at begin. Index and ending at the end of this string • String substring(int begin. Index, int end. Index) – Returns a new string that is a substring of this string, starting at begin. Index and ending at index end. Index - 1 – The length of the substring is end. Index-begin. Index

Useful String methods VI • String to. Upper. Case() – Returns a new String similar to this String, in which all letters are uppercase • String to. Lower. Case() – Returns a new String similar to this String, in which all letters are lowercase • String trim() – Returns a new String similar to this String, but with whitespace removed from both ends

Finally, a useless String method • String to. String() – Returns this String • Why do we have this method? – Consistency--Every Object has a to. String() method

Strings are immutable • A String, once created, cannot be changed • None of the preceding methods modify the String, although several create a new String • Statements like this create new Strings: my. String = my. String + another. Character; • Creating a few extra Strings in a program is no big deal • Creating a lot of Strings can be very costly

Strings, Etc. Part II: String. Buffers

About String. Buffers • A String. Buffer has a capacity (the number of characters it can hold) and a length (the number of characters it is currently holding) • If the capacity is exceeded, the String. Buffer is copied to a new location with more room • String. Buffers are used to implement String concatenation

String. Buffer constructors • String. Buffer() – Constructs a String. Buffer with a capacity of 16 characters • String. Buffer(int capacity) – Constructs a String. Buffer with the requested capacity • String. Buffer(String str) – Constructs a String. Buffer containing the String str

Useful String. Buffer methods I • String. Buffer append(X) – Appends X to the end of this String. Buffer – Also (as a convenience) returns this String. Buffer • The append method is so heavily overloaded that it will work with any argument – If the argument is an object, its to. String() method is used to obtain the String to append

Useful String. Buffer methods II • int length() – Returns the number of characters in this String. Buffer • void set. Length(int new. Length) – Sets the number of characters in this String. Buffer – May result in truncation of characters at the end, or addition of null characters

Useful String. Buffer methods III • char. At(int index) – Returns the character at the location index • void set. Char. At(int index, char ch) – Sets the character at location index to ch • String. Buffer reverse() – The sequence of characters in this String. Buffer is replaced by the reverse of this sequence, and also returned as the value of the method

Useful String. Buffer methods IV • String. Buffer insert(int offset, X) – Insert X starting at the location offset in this String. Buffer – Also returns this (modified) String. Buffer as the value of the method – Like append, this method is heavily overloaded • String. Buffer delete. Char. At(int index) – Deletes the character at location index • String. Buffer delete(int start, int end) – Deletes chars at locations start through end-1

Useful String. Buffer methods V • String substring(int start) – Returns a new String of characters from this String. Buffer, from location start up through the end of the String. Buffer • String substring(int start, int end) – Returns a new String of characters from this String. Buffer, from location start up to and including the character at index end-1 – The length of the substring is end-begin • String to. String() – Returns the characters of this String. Buffer as a String

When to use String. Buffers • If you make a lot of changes or additions to a String, it is much more efficient to use a String. Buffer • If you are simply examining the contents of a String, then a String is at least as efficient as a String. Buffer • For incidental use (such as creating output lines), use Strings; they are more convenient

Strings, Etc. Part III: String. Tokenizers

About String. Tokenizers • A String. Tokenizer is used to break a string into tokens, such as words • A String. Tokenizer uses delimiters to separate tokens; a String. Tokenizer can be made that will return the delimiters, or discard them • You construct a String. Tokenizer for a particular String, use it for one pass through that String, after which the String. Tokenizer is “used up” • There are only a few methods for String. Tokenizers

String. Tokenizer constructors • String. Tokenizer(String str) – Constructs a tokenizer for String str that uses the default (whitespace) delimiters " tnrf" – Does not return delimiters as tokens • String. Tokenizer(String str, String delim) – Constructs a tokenizer that uses the given delimiters delim – Does not return delimiters as tokens • String. Tokenizer(String str, String delim, boolean return. Delims) – Constructs a tokenizer that uses the given delimiters delim – Returns delimiters as tokens if return. Delims is true

String. Tokenizer methods • boolean has. More. Tokens() – Returns true if this tokenizer’s String has more tokens • String next. Token() – Returns the next token • String next. Token(String delim) – Permanently changes this tokenizer’s set of delimiters to delim, then returns the next token • int count. Tokens() – Returns the number of tokens remaining

Example use of String. Tokenizer st = new String. Tokenizer("this is a test"); while (st. has. More. Tokens()) { System. out. println(st. next. Token()); } • Output: this is a test

Strings, Etc. Part IV: Stream. Tokenizers

About Stream. Tokenizers • A Stream. Tokenizer does the same basic things as a String. Tokenizer, but takes its input from an input stream • A Stream. Tokenizer can recognize identifiers, numbers, quoted strings, and various comment styles • Stream. Tokenizers are complex and powerful • We won’t be doing anything with Stream. Tokenizers beyond noting their existence

The End