Download - String Class in Java
String Class in Java
• java.lang Class String
• java.lang.Object java.lang.String
• We do not have to import the String class since it comes from java.lang.
• An object of the String class represents a string of characters. “abcde”;
Two ways to create a String object
• Create a String literal:
String str = "abc";
• With the key word new since it is an object
String str = new String(“abc”);
10-3
Empty Strings• An empty string has no characters;
• Its contents are “null”.
String s1 = “"; String s2 = new String();
Empty strings
String indexes
• String is a sequence of characters.
Each letter in the string has its own index location and can be accessed by it.
index location
10-4
0 1 2 3 4 5 6 7
c o m p u t e r
The length of the String is how many letters it contains: 8The last index of the String is length – 1; 7
10-5
Index locations Index locations are from 0 to length-1
String s = “strawberry”;
strawberry // 10 letters in the word
// index from 0 to 9
int len = s.length() // 10
int lastIndex = s.length()-1 //9
S is the String object I created. Objects call methods with a dot operator.
10-6
String Methods: • Page 78
• There are many ways to manipulate Strings.
• Look on page 78 those tested on AP
• You always use the period to separate the object from the method.
• int len = s1.length();
10-7
Methods — length()
int length (); returns an int
• Returns the number of characters in the string
6
4
int lenF = f.length();
int lenW = w.length();
Returns:
String f = “Flower”;
String w = “Wind”;
10-8
Methods — substring
String s2 = s.substring (i, k);
returns the substring of chars in positions from i to k-1
String s3 = s.substring (i);
returns the substring from i char to the end
String s = “strawberry”;
rawrawberry
String s2 = s.substring (2,5); start at 2 end at 4 String s3 = s.substring (2); start at 2 thru end
Returns:
strawberry
i k
strawberry
i
Strings have index locations from 0 to length-1
String n = “computer";
String one = n.substring(0,7);
String two = n.substring(1,6);
String three = n.substring(2,5);
String four = n.substring(4);
String five = n.substring(3);
String six = n.substring(1,n.length()-2);
String seven = six.substring(0, n.length()/2);
10-9
0 1 2 3 4 5 6 7
c o m p u t e r
s.substring(i, k);returns the substring of chars in positions from i to k-1
s.substring(i);returns the substring from i char to the end
10-10
Methods — Concatenation
String s1 = “obi”;String s2 = “wan”;
String result = s1 + s2;obiwan
String result = s1.concat (s2);the same as s1 + s2 obiwan
10-11
Methods — Find (indexOf)
String date ="July 5, 2012 1:28:19 PM";
date.indexOf ('J'); 0
date.indexOf ('2'); 8
date.indexOf ("2012"); 8
date.indexOf ('2', 9); 11
date.indexOf ("2020"); -1
date.lastIndexOf ('2'); 15
Returns:
(not found)
(starts searching at position 9)
0 8 11 15
Index of return the index location of the first occurrence of the character requested.