May 4, 1998 CS102-02 Lecture 6-1

Stringing Along in Java

CS 102-02

Lecture 6-1

A Java Class in Action

May 4, 1998 CS102-02 Lecture 6-1

Today in a Nutshell

• Characters and strings

• Methods on strings

• Substrings

• Buffered strings

May 4, 1998 CS102-02 Lecture 6-1

"What’s a String?"• A string is a bunch of characters treated

as a single unit

• Characters are the building blocks– ASCII is a 7-bit encoding (variations are 8-

bit)– Unicode is a 16-bit encoding

May 4, 1998 CS102-02 Lecture 6-1

Global Strings• Globalization makes characters

complicated

• Locales– Locale object represents a specific

geographical, political, or cultural region

– Locale-sensitive operations use a Locale object to tailor information for the user

• Example: Displaying a number

May 4, 1998 CS102-02 Lecture 6-1

Strings in Java

• String is a class in Java

• Strings are constant (values cannot be changed after they are created)

• Set of characters "Lisa Simpson" is an anonymous string (aka, string constant or literal string)

• "A" is a string, 'A' is a character

May 4, 1998 CS102-02 Lecture 6-1

Here, There and Everywhere

• Strings are very common in programming– Text is everywhere– Strings are good for short pieces of text

• String manipulation– Find the length of strings– Extract characters– Compare strings

May 4, 1998 CS102-02 Lecture 6-1

How Long?• Use length() to find out how long a

string isString test;

test = new String("The quick, brown");

System.out.println("Length of test is: "

+ test.length());

• Works on anonymous strings too:System.out.println("'Lisa Simpson' is: "

+ "Lisa Simpson".length() +

" characters long.");

May 4, 1998 CS102-02 Lecture 6-1

Strings are Character Sequences• Grab individual characters with charAt()public char charAt(int index)

• A quick example:for (int nextChar = 0; nextChar < test.length();

nextChar++) {

g.drawString(test.charAt(nextChar), xPos,

yPos+(15*nextChar));

}

May 4, 1998 CS102-02 Lecture 6-1

More for Your Money• Get more than one character at atime

with getChars()public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin)

• Copies characters from this string into the destination character array.

• First character is at index srcBegin• Last character to be copied is at index srcEnd-1

• Subarray of dst starting at index dstBegin and ending at index:dstbegin + (srcEnd-srcBegin) - 1

May 4, 1998 CS102-02 Lecture 6-1

Comparing Strings

• What do the concepts ==, <= and >= mean for strings?

• Compare initial characters in a string– Different than numbers– Upper and lower case

• Java uses lexicographic ordering

May 4, 1998 CS102-02 Lecture 6-1

Comparing Strings

• Are two strings equal (including upper and lower case)?

public boolean equals(Object anObject)

"ABC".equals("ABC") is true

"ABC".equals("abc") is false

• If you want to ignore case, use:public boolean equalsIgnoreCase(String anotherString)

May 4, 1998 CS102-02 Lecture 6-1

==, < or > ?

• Comparing two strings:public int compareTo(String anotherString)

– 0 if the argument string is equal to this string

– Less than 0 if this string is lexicographically less than the string argument

– Greater than 0 if this string is lexicographically greater than the string argument

May 4, 1998 CS102-02 Lecture 6-1

Comparing Substrings

• Use regionMatches to heck for equality within two strings

public boolean regionMatches(int toffset, String other, int ooffset, int len)

• Example"A quick, brown fox".regionMatches(7, "An old, brown banana", 6, 7)

May 4, 1998 CS102-02 Lecture 6-1

Comparing Regions

"A quick, brown fox"

0123456789

"An old, brown banana"

Offset == 7

Offset == 6

Length == 7

May 4, 1998 CS102-02 Lecture 6-1

Finding the Substring of Your Dreams

• Find characters (and sequences of characters) within strings

• Looking for characters?indexOf(int)

indexOf(int, int)

indexOf(String)

indexOf(String, int)

lastIndexOf(int) lastIndexOf(int, int) lastIndexOf(String) lastIndexOf(String, int)

May 4, 1998 CS102-02 Lecture 6-1

Getting the Index

• Examples

"abcdefabc".indexOf((int) 'c') is 2

"abcdefabc".indexOf("bc") is 1

"abcdefabc".lastIndexOf("bc") is 7

"abcdefabc".indexOf((int) 'a', 5)

is 6

May 4, 1998 CS102-02 Lecture 6-1

Substrings

• A substring is a string within a string

• Two substring methods– public String substring(int beginIndex) Starts with index and grabs the remainder of the string

– public String substring(int beginIndex, int endIndex)

• Includes character at beginIndex, but not the character at endIndex

May 4, 1998 CS102-02 Lecture 6-1

The String's the Thing• Strings are an easily understandable

format

• Need to convert a variable to something readable? Try valueOf()!boolean char char[] char[], int, int double

float int long Object

– For Object, valueOf() returns the same as obj.toString()

• A string that "textually represents" this object

May 4, 1998 CS102-02 Lecture 6-1

Replacing String Characters

• Replace one character with another in a new stringreplace(char oldChar, char newChar)

Example:

String name =

"Babe, toe soeep-oerding pig";

name.replace('o', 'h');

May 4, 1998 CS102-02 Lecture 6-1

Case Conversion

• Make a copy of a string, all in one case– Handy for enforcing consistency: always

switch strings to upper case or lower casepublic String toLowerCase(Locale locale)

public String toLowerCase()

public String toUpperCase(Locale locale)

public String toUpperCase()

May 4, 1998 CS102-02 Lecture 6-1

Trimming Away Excess String• Throw away leading and trailing

whitespace– Makes matching more reliable

public String trim()

– All characters that have codes less than or equal to '\u0020' (the space character) are considered to be white space

May 4, 1998 CS102-02 Lecture 6-1

Buffer the String Slayer

• Strings are immutable objects– Methods that seem to modify a string

actually create a new string object

• Buffered strings can be modified– Buffered strings have two "lengths"

• Current length of the string• Buffer length (capacity)

May 4, 1998 CS102-02 Lecture 6-1

More on String Buffers

• Strings buffers are great when you need to do extensive string manipulation

• Handy for communications between programs– Two programs can communicate with one

another (for example, email)– Store incoming and outgoing messages in

buffers