08 Slide

Chapter 8 Strings and Text I/O

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Objectives ✦ ✦ ✦ ✦ ✦ ✦ ✦ ✦ ✦ ✦

To use the String class to process fixed strings (§8.2). To use the Character class to process a single character (§8.3). To use the StringBuilder/StringBuffer class to process flexible strings (§8.4). To know the differences between the String, StringBuilder, and StringBuffer classes (§8.2-8.4). To learn how to pass strings to the main method from the command line (§8.5). (Optional) To use the regular expressions to represent patterns for matching, replacing, and splitting strings (§8.6). To discover file properties, delete and rename files using the File class (§8.7). To write data to a file using the PrintWriter class (§8.8.1). To read data from a file using the Scanner class (§8.8.2). (Optional GUI) To add components to a frame (§8.9). Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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The String Class ✦

Constructing a String: – String message = "Welcome to Java“; – String message = new String("Welcome to Java“);

– String s = new String(); ✦ ✦ ✦ ✦ ✦ ✦ ✦ ✦

Obtaining String length and Retrieving Individual Characters in a string String Concatenation (concat) Substrings (substring(index), substring(start, end)) Comparisons (equals, compareTo) String Conversions Finding a Character or a Substring in a String Conversions between Strings and Arrays Converting Characters and Numeric Values to Strings Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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java.lang.String +String()

Constructs an empty string

+String(value: String)

Constructs a string with the specified string literal value

+String(value: char[])

Constructs a string with the specified character array

+charAt(index: int): char

Returns the character at the specified index from this string

+compareTo(anotherString: String): int

Compares this string with another string +compareToIgnoreCase(anotherString: String): int Compares this string with another string ignoring case +concat(anotherString: String): String Concat this string with another string +endsWith(suffix: String): boolean

Returns true if this string ends with the specified suffix

+equals(anotherString: String): boolean

Returns true if this string is equal to anther string +equalsIgnoreCase(anotherString: String): boolean Checks if this string equals anther string ignoring case +getChars(int srcBegin, int srcEnd, char[] dst, int Copies characters from this string into the destination character dstBegin): void array +indexOf(ch: int): int Returns the index of the first occurrence of ch +indexOf(ch: int, fromIndex: int): int

Returns the index of the first occurrence of ch after fromIndex

+indexOf(str: String): int

Returns the index of the first occurrence of str

+indexOf(str: String, fromIndex: int): int

Returns the index of the first occurrence of str after fromIndex

+lastIndexOf(ch: int): int

Returns the index of the last occurrence of ch

+lastIndexOf(ch: int, fromIndex: int): int

Returns the index of the last occurrence of ch before fromIndex

+lastIndexOf(str: String): int

Returns the index of the last occurrence of str

+lastIndexOf(str: String, fromIndex: int): int

Returns the index of the last occurrence of str before fromIndex

+regionMatches(toffset: int, other: String, offset: int, len: int): boolean

Returns true if the specified subregion of this string exactly matches the specified subregion of the string argument

+length(): int

Returns the number of characters in this string

+replace(oldChar: char, newChar: char): String

Returns a new string with oldChar replaced by newChar

+startsWith(prefix: String): boolean

Returns true if this string starts with the specified prefix

+subString(beginIndex: int): String

Returns the substring from beginIndex

+subString(beginIndex: int, endIndex: int): String

Returns the substring from beginIndex to endIndex-1.

+toCharArray(): char[]

Returns a char array consisting characters from this string

+toLowerCase(): String

Returns a new string with all characters converted to lowercase

+toString(): String

Returns a new string with itself

+toUpperCase(): String

Returns a new string with all characters converted to uppercase

+trim(): String

Returns a string with blank characters trimmed on both sides

+copyValueOf(data: char[]): String

Returns a new string consisting of the char array data

+valueOf(c: char): String

Returns a string consisting of the character c

+valueOf(data: char[]): String

Same as copyValueOf(data: char[]): String

+valueOf(d: double): String

Returns a string representing the double value

+valueOf(f: float): String

Returns a string representing the float value

+valueOf(i: int): String Liang, Introduction to

+valueOf(l: long): String

ReturnsEdition, a string representing int valueEducation, Inc. All Java Programming, Sixth (c) 2007 the Pearson Returns a string representing the long value rights reserved. 0-13-222158-6

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Constructing Strings String newString = new String(stringLiteral); String message = new String("Welcome to Java"); Since strings are used frequently, Java provides a shorthand initializer for creating a string: String message = "Welcome to Java"; Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Strings Are Immutable A String object is immutable; its contents cannot be changed. Does the following code change the contents of the string? String s = "Java"; s = "HTML";

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6

animation

Trace Code

String s = "Java"; s = "HTML";

After executing s = "HTML";

After executing String s = "Java"; s

: String String object for "Java"

Contents cannot be changed

s

: String String object for "Java"

This string object is now unreferenced

: String String object for "HTML"

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

7

animation

Trace Code String s = "Java"; s = "HTML"; After executing s = "HTML";

After executing String s = "Java"; s

: String String object for "Java"

Contents cannot be changed

s

: String String object for "Java"

This string object is now unreferenced

: String String object for "HTML"

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Finding String Length Finding string length using the length() method: message = "Welcome"; message.length() (returns 7)

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9

Retrieving Individual Characters in a String ✦

Do not use message[0]

✦

Use message.charAt(index)

✦

Index starts from 0

Indices

0

1

2

3

4

5

6

message

W

e

l

c

o

m

e

message.charAt(0)

7

8

9

t

o

message.length() is 15

10 11 12 13 14 J

a

v

a

message.charAt(14)

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String Concatenation String s3 = s1.concat(s2);

String s3 = s1 + s2; s1 + s2 + s3 + s4 + s5 same as (((s1.concat(s2)).concat(s3)).concat(s4)).concat(s5);

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Extracting Substrings You can extract a single character from a string using the charAt method. You can also extract a substring from a string using the substring method in the String class. String s1 = "Welcome to Java"; String s2 = s1.substring(0, 11) + "HTML";

Indices

0

1

2

3

4

5

6

message

W

e

l

c

o

m

e

7

8

9

t

o

message.substring(0, 11)

10 11 12 13 14 J

a

v

a

message.substring(11)

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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String Comparisons ✦

equals String s1 = new String("Welcome“); String s2 = "welcome"; if (s1.equals(s2)){ // s1 and s2 have the same contents

} if (s1 == s2) { // s1 and s2 have the same reference

} Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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String Comparisons, cont. ✦

compareTo(Object object) String s1 = new String("Welcome“); String s2 = "welcome"; if (s1.compareTo(s2) > 0) { // s1 is greater than s2 } else if (s1.compareTo(s2) == 0) { // s1 and s2 have the same contents } else // s1 is less than s2 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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String Conversions The contents of a string cannot be changed once the string is created. But you can convert a string to a new string using the following methods: ✦ ✦ ✦ ✦

toLowerCase toUpperCase trim replace(oldChar, newChar) Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Finding a Character or a Substring in a String "Welcome "Welcome "Welcome "Welcome "Welcome "Welcome "Welcome

to to to to to to to

Java".indexOf('W') returns 0. Java".indexOf('x') returns -1. Java".indexOf('o', 5) returns 9. Java".indexOf("come") returns 3. Java".indexOf("Java", 5) returns 11. Java".indexOf("java", 5) returns -1. Java".lastIndexOf('a') returns 14.

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16

Convert Character and Numbers to Strings The String class provides several static valueOf methods for converting a character, an array of characters, and numeric values to strings. These methods have the same name valueOf with different argument types char, char[], double, long, int, and float. For example, to convert a double value to a string, use String.valueOf(5.44). The return value is string consists of characters ‘5’, ‘.’, ‘4’, and ‘4’. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Example: Finding Palindromes ✦ Objective:

Checking whether a string is a palindrome: a string that reads the same forward and backward. CheckPalindrome

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18

The Character Class java.lang.Character +Character(value: char)

Constructs a character object with char value

+charValue(): char

Returns the char value from this object

+compareTo(anotherCharacter: Character): int

Compares this character with another

+equals(anotherCharacter: Character): boolean Returns true if this character equals to another +isDigit(ch: char): boolean Returns true if the specified character is a digit +isLetter(ch: char): boolean

Returns true if the specified character is a letter

+isLetterOrDigit(ch: char): boolean

Returns true if the character is a letter or a digit

+isLowerCase(ch: char): boolean

Returns true if the character is a lowercase letter

+isUpperCase(ch: char): boolean

Returns true if the character is an uppercase letter

+toLowerCase(ch: char): char

Returns the lowercase of the specified character

+toUpperCase(ch: char): char

Returns the uppercase of the specified character

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Examples Character charObject = new Character('b'); charObject.compareTo(new Character('a')) returns 1 charObject.compareTo(new Character('b')) returns 0 charObject.compareTo(new Character('c')) returns -1 charObject.compareTo(new Character('d') returns –2 charObject.equals(new Character('b')) returns true charObject.equals(new Character('d')) returns false

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Example: Counting Each Letter in a String This example gives a program that counts the number of occurrence of each letter in a string. Assume the letters are not case-sensitive.

CountEachLetter

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21

StringBuilder and StringBuffer The StringBuilder/StringBuffer class is an alternative to the String class. In general, a StringBuilder/StringBuffer can be used wherever a string is used. StringBuilder/StringBuffer is more flexible than String. You can add, insert, or append new contents into a string buffer, whereas the value of a String object is fixed once the string is created.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

22

StringBuilder vs. StringBuffer The StringBuilder class, introduced in JDK 1.5, is similar to StringBuffer except that the update methods in StringBuffer are synchronized. Use StringBuffer if it may be accessed by multiple tasks concurrently. Using StringBuilder is more efficient if it is accessed by a single task. The constructors and methods in StringBuffer and StringBuilder are almost the same. This book covers StringBuffer. You may replace StringBuffer by StringBuilder. The program can compile and run without any other changes. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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The StringBuffer Class The StringBuffer class is an alternative to the String class. In general, a string buffer can be used wherever a string is used. StringBuffer is more flexible than String.

You can add, insert, or append new contents into a string buffer. However, the value of a String object is fixed once the string is created.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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java.lang.StringBuffer +StringBuffer()

Constructs an empty string buffer with capacity 16

+StringBuffer(capacity: int)

Constructs a string buffer with the specified capacity

+StringBuffer(str: String)

Constructs a string buffer with the specified string

+append(data: char[]): StringBuffer

Appends a char array into this string buffer

+append(data: char[], offset: int, len: int): StringBuffer

Appends a subarray in data into this string buffer

+append(v: aPrimitiveType): StringBuffer

Appends a primitive type value as string to this buffer

+append(str: String): StringBuffer

Appends a string to this string buffer

+capacity(): int

Returns the capacity of this string buffer

+charAt(index: int): char

Returns the character at the specified index

+delete(startIndex: int, endIndex: int): StringBuffer

Deletes characters from startIndex to endIndex

+deleteCharAt(int index): StringBuffer

Deletes a character at the specified index

+insert(index: int, data: char[], offset: int, len: int): StringBuffer

Inserts a subarray of the data in the array to the buffer at the specified index

+insert(offset: int, data: char[]): StringBuffer

Inserts data to this buffer at the position offset

+insert(offset: int, b: aPrimitiveType): StringBuffer

Inserts a value converted to string into this buffer

+insert(offset: int, str: String): StringBuffer

Inserts a string into this buffer at the position offset

+length(): int

Returns the number of characters in this buffer

+replace(int startIndex, int endIndex, String str): StringBuffer

Replaces the characters in this buffer from startIndex to endIndex with the specified string

+reverse(): StringBuffer

Reveres the characters in the buffer

+setCharAt(index: int, ch: char): void

Sets a new character at the specified index in this buffer

+setLength(newLength: int): void

Sets a new length in this buffer

+substring(startIndex: int): String

Returns a substring starting at startIndex

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StringBuffer Constructors ✦

public StringBuffer() No characters, initial capacity 16 characters.

✦

public StringBuffer(int length) No characters, initial capacity specified by the length argument.

✦

public StringBuffer(String str) Represents the same sequence of characters as the string argument. Initial capacity 16 plus the length of the string argument.

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Appending New Contents into a String Buffer StringBuffer strBuf = new StringBuffer(); strBuf.append("Welcome"); strBuf.append(' '); strBuf.append("to"); strBuf.append(' '); strBuf.append("Java");

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Example: Checking Palindromes Ignoring Non-alphanumeric Characters This example gives a program that counts the number of occurrence of each letter in a string. Assume the letters are not case-sensitive. PalindromeIgnoreNonAlphanumeric

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Main Method Is Just a Regular Method You can call a regular method by passing actual parameters. Can you pass arguments to main? Of course, yes. For example, the main method in class B is invoked by a method in A, as shown below: public class A { public static void main(String[] args) { String[] strings = {"New York", "Boston", "Atlanta"}; B.main(strings); } }

class B { public static void main(String[] args) { for (int i = 0; i < args.length; i++) System.out.println(args[i]); } }

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Command-Line Parameters class TestMain { public static void main(String[] args) { ... } } java TestMain arg0 arg1 arg2 ... argn

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Processing Command-Line Parameters In the main method, get the arguments from args[0], args[1], ..., args[n], which corresponds to arg0, arg1, ..., argn in the command line.

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31

Example: Using Command-Line Parameters ✦

Objective: Write a program that will perform binary operations on integers. The program receives three parameters: an operator and two integers. java Calculator 2 + 3 Calculator

java Calculator 2 - 3 java Calculator 2 / 3 java Calculator 2 “*” 3

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

32

Pedagogical NOTE The previous edition of this book introduced the StringTokenizer class for extracting tokens from a string. Using regular expressions is more powerful and flexible than StringTokenizer for splitting strings. Therefore, StringTokenizer is obsolete.

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33

Optional

Regular Expressions

A regular expression (abbreviated regex) is a string that describes a pattern for matching a set of strings. Regular expression is a powerful tool for string manipulations. You can use regular expressions for matching, replacing, and splitting strings.

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34

Optional

Matching Strings

"Java".matches("Java"); "Java".equals("Java");

"Java is fun".matches("Java.*") "Java is cool".matches("Java.*") "Java is powerful".matches("Java.*")

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35

Optional

Regular Expression Syntax Regular Expression x . (ab|cd) [abc] [^abc]

Matches

Example

a specified character x any single character a, b, or c a, b, or c any character except a, b, or c a through z any character except a through z a through e or m through p intersection of a-e with c-p

Java matches Java Java matches J..a ten matches t(en|im] Java matches Ja[uvwx]a Java matches Ja[^ars]a

\d \D \w \W \s \S

a a a a a a

Java2 matches "Java[\\d]" $Java matches "[\\D][\\D]ava" Java matches "[\\w]ava" $Java matches "[\\W][\\w]ava" "Java 2" matches "Java\\s2" Java matches "[\\S]ava"

p*

zero or more occurrences of pattern p one or more occurrences of pattern p zero or one occurrence of pattern p exactly n occurrences of pattern p at least n occurrences of pattern p between n and m occurrences (inclusive)

[a-z] [^a-z] [a-e[m-p]] [a-e&&[c-p]]

p+ p? p{n} p{n,} p{n,m}

digit, same as [1-9] non-digit word character non-word character whitespace character non-whitespace char

Java matches [A-M]av[a-d] Java matches Jav[^b-d] Java matches [A-G[I-M]]av[a-d] Java matches [A-P&&[I-M]]av[a-d]

Java matches "[\\w]*" Java matches "[\\w]+" Java matches "[\\w]?Java" Java matches "[\\w]?ava" Java matches "[\\w]{4}" Java matches "[\\w]{3,}" Java matches "[\\w]{1,9}"

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

36

Optional

Replacing and Splitting Strings java.lang.String

+matches(regex: String): boolean

Returns true if this string matches the pattern.

+replaceAll(regex: String, replacement: String): String

Returns a new string that replaces all matching substrings with the replacement.

+replaceFirst(regex: String, replacement: String): String

Returns a new string that replaces the first matching substring with the replacement.

+split(regex: String): String[]

Returns an array of strings consisting of the substrings split by the matches.

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37

Examples String s = "Java Java Java".replaceAll("v\\w", "wi") ; String s = "Java Java Java".replaceFirst("v\\w", "wi") ; String[] s = "Java1HTML2Perl".split("\\d");

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

38

Pedagogical NOTE The previous edition of this book introduced text I/O using many subclasses of java.io.Writer and java.io.Reader. These classes are lower-level and difficult to learn. The java.util.PrintWriter and java.util.Scanner classes are higher-level and easy to use. All the programs written using the lower-level text I/O classes can be revised using the PrintWriter and Scanner classes. Therefore, the PrintWriter and Scanner classes supersede the lower-level text I/O classes. If students need to know these lower-level text I/O classes, please refer to Supplement V.I, “Text I/O Using Reader and Writer.” Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

39

The File Class The File class is intended to provide an abstraction that deals with most of the machine-dependent complexities of files and path names in a machine-independent fashion. The filename is a string. The File class is a wrapper class for the file name and its directory path.

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Obtaining file properties and manipulating file

java.io.File +File(pathname: String)

Creates a File object for the specified pathname. The pathname may be a directory or a file.

+File(parent: String, child: String) Creates a File object for the child under the directory parent. child may be a filename or a subdirectory. +File(parent: File, child: String) Creates a File object for the child under the directory parent. parent is a File object. In the preceding constructor, the parent is a string. +exists(): boolean Returns true if the file or the directory represented by the File object exists. +canRead(): boolean

Returns true if the file represented by the File object exists and can be read.

+canWrite(): boolean

Returns true if the file represented by the File object exists and can be written.

+isDirectory(): boolean

Returns true if the File object represents a directory.

+isFile(): boolean

Returns true if the File object represents a file.

+isAbsolute(): boolean

Returns true if the File object is created using an absolute path name.

+isHidden(): boolean

Returns true if the file represented in the File object is hidden. The exact definition of hidden is system-dependent. On Windows, you can mark a file hidden in the File Properties dialog box. On Unix systems, a file is hidden if its name begins with a period character '.'.

+getAbsolutePath(): String

Returns the complete absolute file or directory name represented by the File object.

+getCanonicalPath(): String

Returns the same as getAbsolutePath() except that it removes redundant names, such as "." and "..", from the pathname, resolves symbolic links (on Unix platforms), and converts drive letters to standard uppercase (on Win32 platforms).

+getName(): String

Returns the last name of the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getName() returns test.dat.

+getPath(): String

Returns the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getPath() returns c:\book\test.dat.

+getParent(): String

Returns the complete parent directory of the current directory or the file represented by the File object. For example, new File("c:\\book\\test.dat").getParent() returns c:\book.

+lastModified(): long

Returns the time that the file was last modified.

+delete(): boolean

Deletes this file. The method returns true if the deletion succeeds.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All +renameTo(dest: File): boolean Renames this file. The method returns true if the operation succeeds. rights reserved. 0-13-222158-6

41

Example: Using the File Class Objective: Write a program that demonstrates how to create files in a platform-independent way and use the methods in the File class to obtain their properties. Figure 16.1 shows a sample run of the program on Windows, and Figure 16.2 a sample run on Unix.

TestFileClass

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42

Text I/O A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate Java I/O classes. The objects contain the methods for reading/writing data from/to a file. This section introduces how to read/write strings and numeric values from/to a text file using the Scanner and PrintWriter classes.

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43

Writing Data Using PrintWriter java.io.PrintWriter +PrintWriter(filename: String)

Creates a PrintWriter for the specified file.

+print(s: String): void

Writes a string.

+print(c: char): void

Writes a character.

+print(cArray: char[]): void

Writes an array of character.

+print(i: int): void

Writes an int value.

+print(l: long): void

Writes a long value.

+print(f: float): void

Writes a float value.

+print(d: double): void

Writes a double value.

+print(b: boolean): void

Writes a boolean value.

Also contains the overloaded println methods.

A println method acts like a print method; additionally it prints a line separator. The line separator string is defined by the system. It is \r\n on Windows and \n on Unix. The printf method was introduced in §3.6, “Formatting Console Output and Strings.”

Also contains the overloaded printf methods. .

WriteData Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

44

Reading Data Using Scanner java.util.Scanner +Scanner(source: File)

Creates a Scanner that produces values scanned from the specified file.

+Scanner(source: String)

Creates a Scanner that produces values scanned from the specified string.

+close()

Closes this scanner.

+hasNext(): boolean

Returns true if this scanner has another token in its input.

+next(): String

Returns next token as a string.

+nextByte(): byte

Returns next token as a byte.

+nextShort(): short

Returns next token as a short.

+nextInt(): int

Returns next token as an int.

+nextLong(): long

Returns next token as a long. Returns next token as a float.

+nextFloat(): float +nextDouble(): double +useDelimiter(pattern: String): Scanner

Returns next token as a double. Sets this scanner’s delimiting pattern.

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Example: Replacing Text Write a class named ReplaceText that replaces a string in a text file with a new string. The filename and strings are passed as command-line arguments as follows: java ReplaceText sourceFile targetFile oldString newString

For example, invoking java ReplaceText FormatString.java t.txt StringBuilder StringBuffer

replaces all the occurrences of StringBuilder by StringBuffer in FormatString.java and saves the new file in t.txt. ReplaceText Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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The StringTokenizer Class java.util.StringTokenizer +StringTokenizer(s: String)

Constructs a string tokenizer for the string.

+StringTokenizer(s: String, delimiters: Constructs a string tokenizer for the string with the specified delimiters. String) +StringTokenizer(s: String, delimiters: Constructs a string tokenizer for the string with the delimiters and returnDelims. String, returnDelimiters: boolean) Returns the number of remaining tokens. +countTokens(): int +hasMoreTokens(): boolean

Returns true if there are more tokens left.

+nextToken(): String

Returns the next token.

+nextToken(delimiters: String): String Returns the next token using new delimiters.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Examples 1 String s = "Java is cool."; StringTokenizer tokenizer = new StringTokenizer(s); System.out.println("The total number of tokens is " + tokenizer.countTokens()); while (tokenizer.hasMoreTokens()) System.out.println(tokenizer.nextToken());

The code displays

The total number of tokens is 3 Java is cool.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Examples 2 String s = "Java is cool."; StringTokenizer tokenizer = new StringTokenizer(s, "ac"); System.out.println("The total number of tokens is " + tokenizer.countTokens()); while (tokenizer.hasMoreTokens()) System.out.println(tokenizer.nextToken());

The code displays

The total number of tokens is 4 J v is ool.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Examples 3

String s = "Java is cool."; StringTokenizer tokenizer = new StringTokenizer(s, "ac", ture); System.out.println("The total number of tokens is " + tokenizer.countTokens()); while (tokenizer.hasMoreTokens()) System.out.println(tokenizer.nextToken());

The code displays

The total number of tokens is 7 J a v a is c ool.

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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JDK 1.5 Feature

The Scanner Class

The delimiters are single characters in StringTokenizer. You can use the new JDK 1.5 java.util.Scanner class to specify a word as a delimiter. String s = "Welcome to Java! Java is fun! Java is cool!"; Scanner scanner = new Scanner(s); scanner.useDelimiter("Java");

Creates an instance of Scanner for the string.

Sets “Java” as a delimiter. while (scanner.hasNext()) System.out.println(scanner.next());

Welcome to ! is fun! is cool!

hasNext() returns true if there are still more tokens left. The next() method returns a token as a string. Output

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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JDK 1.5 Feature

Scanning Primitive Type Values

If a token is a primitive data type value, you can use the methods nextByte(), nextShort(), nextInt(), nextLong(), nextFloat(), nextDouble(), or nextBoolean() to obtain it. For example, the following code adds all numbers in the string. Note that the delimiter is space by default. String s = "1 2 3 4"; Scanner scanner = new Scanner(s); int sum = 0; while (scanner.hasNext()) sum += scanner.nextInt(); System.out.println("Sum is " + sum);

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

52

JDK 1.5 Feature

Console Input Using Scanner

Another important application of the Scanner class is to read input from the console. For example, the following code reads an int value from the keyboard: System.out.print("Please enter an int value: "); Scanner scanner = new Scanner(System.in); int i = scanner.nextInt();

NOTE: StringTokenizer can specify several single characters as delimiters. Scanner can use a single character or a word as the delimiter. So, if you need to scan a string with multiple single characters as delimiters, use StringTokenizer. If you need to use a word as the delimiter, use Scanner. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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