1. String StringBuffer

2. class StringExample { public static void main (String[] args) { String str1 = "Seize the day"; String str2 = new String(); String str3 = new String(str1); String str4 = "Day of the seize"; String str5 = "Seize the day"; System.out.println("str1: " + str1); // str1: Seize the day System.out.println("str2: " + str2); // str2: System.out.println("str3: " + str3); // str3: Seize the day System.out.println("str4: " + str4); // str4: Day of the seize System.out.println("str5: " + str5); // str5: Seize the day System.out.println(); System.out.println("length of str1 is " + str1.length()); //length of str1 is 13 System.out.println("length of str2 is " + str2.length()); //length of str2 is 0 System.out.println();

3. System.out.println("Index of 'e' in str4: " + str4.indexOf('e')); // Index of 'e' in str4: 9 System.out.println("Char at pos 3 in str1: " + str1.charAt(3)); //Char at pos 3 in str1: z System.out.println("Substring 6 to 8 of str1: " + str1.substring(6,8)); // Substring 6 to 8 of str1: th if (str1==str5) System.out.println("str1 and str5 refer to the “ + “same object"); //str1 and str5 refer to the same object if (str1 != str3) System.out.println("str1 and str3 don't refer to “ + “the same object"); //str1 and str3 don't refer to the same object if (str1.equals(str3)) System.out.println("str1 and str3 contain the “ + ”same chars"); //str1 and str3 contain the same chars System.out.println();

4. str2 = str1.toUpperCase(); System.out.println("str2 now is: " + str2); //str2 now is: SEIZE THE DAY str5 = str1.replace('e','X'); System.out.println("str5 is now: " + str5); //str5 is now: SXizX thX day //now check again if (str1==str5) System.out.println("str1 and str5 refer to the “ + “same object"); else System.out.println("str1 and str5 don't refer to “ + “the same object"); //str1 and str5 don't refer to the same object }

5. Useful methods for string: length() :returns the length charAt (int index) :returns char at that positions (0..) indexOf(char ch) :returns index (0..) of first occurrence lastindexOf(char ch) :returns index (0..) of last occurrence endsWith(String suffix):returns true if has this suffix startsWith(String prefix):returns true if has this prefix equals(Object obj) :returns true if two strings are the same equalsIgnoreCase(Object obj) :returns true if two strings are equal, ignoring case toLowerCase() :returns a new string of lower case toUpperCase() :returns a new string of upper case substring(int begin, int end):returns a new string that is a substring of this string including begin, excluding end.

6. java.lang.StringBuffer. StringBuffer- implements a mutable sequence of characters. String - implements a constant sequence of characters. public class ReverseString{ public static void main(String[] args){ String source="abcdefg"; int strLen=source.length(); StringBuffer dest = new StringBuffer( strLen ); for( int i= strLen-1; i>=0; i--){ dest.append( source.charAt(i) ); } System.out.println( dest ); } output: gfedcba