Strings

1. Strings • Can view as array of chartacters • Implemented as a class with its own methods • Simplest operation on strings is catenating two strings String x = “Good”; String y = “Morning!”; String z = x + “ ” + y; String w = x + ‘ ’ + y; // also works • Possible to concatenate strings to variables of other types e.g., int, float, etc. • Internally converted to string

2. Methods of string class • Determining the length of a string String x = “abc”; int lengthOfx = x.length(); • Determining the character at a position String x = “abc”; char cAt2 = x.charAt(2); char first = x.charAt(0); char last = x.charAt(x.length()-1); • Case conversion String x = “Mainak”; String y = x.toUpperCase(); // y is “MAINAK” String z = x.toLowerCase(); // z is “mainak”

3. More on concatenation • Concatenating strings is different from concatenating characters String x = “a”; String y = “b”; String z = x + y; // z is “ab” char x1 = ‘a’; char y1 = ‘b’; char z1 = x1 + y1; // z is not “ab” • For concatenating two strings you can use the concat method also String z = “to”.concat(“get”).concat(“her”);

4. Extracting substrings • Can extract the substring starting at a position String x = “together”; String y = x.substring(2); // y is “gether” String z = x.substring(3); // z is “ether” String w = x.substring(0); // same as x String u = x.substring(x.length()-1); // “r” String v = x.substring(x.length()); // blank • Can extract substring between two positions String y = x.substring(0, 5); // y is “toget” String z = x.substring(5, x.length()); // “her” String w = x.substring(5, 6); // w is “h” String u = x.substring(5, 5); // u is “”

5. Searching in a string • Finding the first occurrence of a character or a substring within a string String x = “abracadabra”; int k = x.indexOf(‘a’); // k is 0 int p = x.indexOf(‘a’, 1); // p is 3; search // begins from pos 1 int t = x.indexOf(‘e’); // t is -1 int q = x.indexOf(“ra”); // q is 2 int s = x.indexOf(“ra”, 3); // s is 9 • Possible to find the last occurrence also int p = x.lastIndexOf(‘r’); // p is 9

6. Comparison of strings • Compares strings in dictionary order (also known as lexicographical order) • Returns zero if strings are equal String x = “abc”; String y = “abcd”; String z = “ab”; String w = “abd”; int p = x.compareTo(y); // p is negative int q = x.compareTo(x); // q is zero int r = x.compareTo(z); // r is positive int s = y.compareTo(w); // s is negative • This comparison is case sensitive • Use compareToIgnoreCase otherwise

7. Some more useful methods • Removing leading and trailing whitespaces String x = “ abc ”; String y = x.trim(); // y is “abc” • Test for prefix String x = “Mainak”; boolean y = x.startsWith(“Main”); // y is true boolean z = x.startsWith(“nak”, 3); // z is true • Test for suffix String x = “Canada”; boolean y = x.endsWith(“ada”); // y is true

8. Some more useful methods • Substitute all occurrences of a character with another character String x = “deer”; String y = x.replace(‘e’, ‘o’); // y is “door” String z = x.replace(‘a’, ‘o’); // z is “deer” • Partial string match String x = “abracadabra”; boolean y = x.regionMatches(true, 2, “bracket”, 1, 3); // y is true • The first argument should be set to true if the match is intended to be case ignorant

9. regionMatches boolean regionMatches(int toffset, String other, int ooffset, int len) • Tests whether the specified region of this string matches the specified region of the String argument. • Region is of length len and begins at the index toffset for this string and ooffset for the other string.

10. regionMatches boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) • Tests whether the specified region of this string matches the specified region of the String argument. Region is of length len and begins at the index toffset for this string and ooffset for the other string. • The boolean argument indicates whether case should be ignored; if true, case is ignored when comparing characters.

11. RegionMatchesDemo public class RegionMatchesDemo { public static void main(String[] args) { String searchMe = "Green Eggs and Ham"; String findMe = "Eggs"; int searchMeLength = searchMe.length(); int findMeLength = findMe.length(); boolean foundIt = false; for (int i = 0; i <= (searchMeLength - findMeLength); i++) { if (searchMe.regionMatches(i, findMe, 0, findMeLength)) { foundIt = true; System.out.println(searchMe.substring(i, i + findMeLength)); break; } } if (!foundIt) System.out.println("No match found."); } }

12. The program steps through the string referred to by searchMe one character at a time. For each character, the program calls the regionMatches method to determine whether the substring beginning with the current character matches the string the program is looking for. • The output from this program is Eggs.