1. MSIS 655 Advanced Business Applications Programming
Week 8
Strings and Characters (Ch. 29)
In this chapter you will learn:
To create and manipulate immutable character string objects of class String.
To create and manipulates mutable character string objects of class StringBuffer.
To create and manipulate objects of class Character.
To use a StringTokenizer object to break a String object into tokens.
To use regular expressions to validate String data entered into an application.
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8.1

2. Introduction String and character processing String
Class java.lang.String
Class java.lang.StringBuffer
Class java.lang.Character
Class java.util.StringTokenizer
String
Series of characters treated as single unit
May include letters, digits, special characters.
Object of class String
String literals
1Java treats all string literals with the same contents as a single String object that has many references to it. This conserves memory.
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3. String Constructors Fig. 29.1 demonstrates four constructors
No-argument constructor
One-argument constructor
A String object
A char array
Three-argument constructor
An integer specifies the starting position
An integer specifies the number of characters to access
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4. String Methods (Fig. 29.2) Method length Method charAt Method getChars
Determine the length of a String
Like arrays, Strings always “know” their size
Unlike array, Strings do not have length instance variable
Method charAt
Get character at specific location in String
Method getChars
Get entire set of characters in String
Method (void)
getChars (int srcBegin, int srcEnd, char[] dst, int dstBegin)    Copies characters from this string into the destination character array.
ex: String s1 = “hello there”;
s1.getChars( 0, 5, charArray, 0);
=> charArray = {“h”, “e”, “l”, “l”, “o”}
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5. Comparing Strings (Fig. 29.3)
Comparing String objects
Method equals
Method equalsIgnoreCase
Method compareTo
Method regionMatches
Comparing references with == can lead to logic errors, because == compares the references to determine whether they refer to the same object, not whether two objects have the same contents. When two identical (but separate) objects are compared with ==, the result will be false. When comparing objects to determine whether they have the same contents, use method equals.
- Method (boolean) regionMatches (int toffset, String other, int ooffset, int len)
Tests if two string regions are equal. A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent identical character sequences. The substring of this String object to be compared begins at index toffset and has length len. The substring of other to be compared begins at index ooffset and has length len. The result is false if and only if at least one of the following is true:
toffset is negative. ooffset is negative. toffset+len is greater than the length of this String object. ooffset+len is greater than the length of the other argument. There is some nonnegative integer k less than len such that: this.charAt(toffset+k) != other.charAt(ooffset+k)
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6. Miscellaneous String Methods
Methods startsWith / endsWith
Methods indexOf / lastIndexOf
Method substring
Method concat
Methods replace / toUpperCase / toLowerCase / trim
Method valueOf
startsWith(String prefix) returns true if the character sequence represented by the argument is a prefix of the character sequence represented by this string; false otherwise.
lastIndexOf(String str): if the string argument occurs one or more times as a substring within this object, then the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.
trim() returns a copy of the string, with leading and trailing whitespace omitted.
"to".concat("get").concat("her") returns "together"
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7. Class StringBuffer Class StringBuffer
When String object is created, its contents cannot change
Used for creating and manipulating dynamic string data
i.e., modifiable Strings
Can store characters based on capacity
Capacity expands dynamically to handle additional characters
Uses operators + and += for String concatenation
In programs that frequently perform string concatenation, or other string modifications, it is more efficient to implement the modifications with class StringBuffer (covered in Section 29.4).
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8. Class Character Treat primitive variables as objects
Type wrapper classes
Boolean
Character
Double
Float
Byte
Short
Integer
Long
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9. Class StringTokenizer
Partition String into individual substrings
Use delimiter
Typically whitespace characters (space, tab, newline, etc)
Java offers java.util.StringTokenizer
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10. Lab activities (Week 8) Exercises (pp. 1392-93) 29.5, 29.7, 29.8,
Advanced: 29.19
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