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4.3 The String and the StringBuffer Class
The String class provided by the Java SDK represents combinations of character literals. Unlike in other programming languages like C or C++, strings can be represented using
an array of characters or by simply using the String class. Take note that a String object differs from an array of characters.
4.3.1 String Constructors
The String class has 11 constructors. To see how some of these constructors, consider the given example that follows.
This example is taken from Dr. Encarnacions notes. class StringConstructorsDemo {
public static void mainString args[] { String s1 = new String; creates an empty string
char chars[] = { h, e, l, l, o}; String s2 = new Stringchars; s2 = hello;
byte bytes[] = { w, o, r, l, d }; String s3 = new Stringbytes;
s3 = world String s4 = new Stringchars, 1, 3;
String s5 = new Strings2; String s6 = s2;
System.out.printlns1; System.out.printlns2;
System.out.printlns3; System.out.printlns4;
System.out.printlns5; System.out.printlns6;
} }
Here is the expected output of the given program: hello
world ell
hello hello
4.3.2 String Methods
The following is a list of some String methods.
String Methods
public char charAtint index Returns the character located in the specified index.
public int compareToString anotherString Compares this string with the specified parameter. Returns a negative value if this
string comes lexicographically before the other string, 0 if both of the strings have the same value and a postive value if this string comes after the other string
lexicographically.
public int compareToIgnoreCaseString str Like compareTo but ignores the case used in this string and the specified string.
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String Methods
public boolean equalsObject anObject Returns true if this string has the same sequence of characters as that of the Object
specified, which should be a String object. Otherwise, if the specified parameter is not a String object or if it doesnt match the sequence of symbols in this string, the method
will return false.
public boolean equalsIgnoreCaseString anotherString Like equals but ignores the case used in this string and the specified string.
public void getCharsint srcBegin, int srcEnd, char[] dst, int dstBegin Gets the characters from this string starting at the srcBegin index up to the srcEnd
index and copies these characters to the dst array starting at the dstBegin index. public int length
Returns the length of this string. public String replacechar oldChar, char newChar
Returns the string wherein all occurrences of the oldChar in this string is replaced with newChar.
public String substringint beginIndex, int endIndex Returns the substring of this string starting at the specified beginIndex index up to the
endIndex index. public char[] toCharArray
Returns the character array equivalent of this string. public String trim
Returns a modified copy of this string wherein the leading and trailing white space are removed.
public static String valueOf- Takes in a simple data type such as boolean, integer or character, or it takes in an
object as a parameter and returns the String equivalent of the specified parameter.
Table 8: Some methods of class String
Consider how these methods were used in the following program. class StringDemo {
public static void mainString args[] { String name = Jonathan;
System.out.printlnname: + name; System.out.println3
rd
character of name: + name.charAt2;
character that first appears alphabetically has lower unicode value
System.out.printlnJonathan compared to Solomon: + name.compareToSolomon;
System.out.printlnSolomon compared to Jonathan: + Solomon.compareToJonathan;
J has lower unicode value compared to j System.out.printlnJonathan compared to jonathan: +
name.compareTojonathan; System.out.printlnJonathan compared to jonathan ignore
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case: + name.compareToIgnoreCasejonathan; System.out.printlnIs Jonathan equal to Jonathan? +
name.equalsJonathan; System.out.printlnIs Jonathan equal to jonathan? +
name.equalsjonathan; System.out.printlnIs Jonathan equal to jonathan ignore
case? + name.equalsIgnoreCasejonathan; char charArr[] = Hi XX.toCharArray;
Need to add 1 to the endSrc index of getChars Jonathan.getChars0, 2, charArr, 3;
System.out.printgetChars method: ; System.out.printlncharArr;
System.out.printlnLength of name: + name.length; System.out.printlnReplace as with es in name: +
name.replacea, e; Need to add 1 to the endIndex parameter of substring
System.out.printlnA substring of name: + name.substring0, 2;
System.out.printlnTrim \ a b c d e f \: \ + a b c d e f .trim + \;
System.out.printlnString representation of boolean expression 1010: + String.valueOf1010;
toString method is implicitly called in the println method
System.out.printlnString representation of boolean expression 1010: + 1010;
Note theres no change in the String object name even after applying all these methods.
System.out.printlnname: + name; }
}
Heres the output of the given program. name: Jonathan
3rd character of name: n Jonathan compared to Solomon: -9
Solomon compared to Jonathan: 9 Jonathan compared to jonathan: -32
Jonathan compared to jonathan ignore case: 0 Is Jonathan equal to Jonathan? true
Is Jonathan equal to jonathan? false Is Jonathan equal to jonathan ignore case? true
content of charArr after getChars method: Hi Jo Length of name: 8
Replace as with es in name: Jonethen A substring of name: Jo
Trim a b c d e f : a b c d e f String representation of boolean expression 1010: false
String representation of boolean expression 1010: false name: Jonathan
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4.3.3 The StringBuffer Class
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