1. 16
Strings

2. Previously
Classes
Methods
Scoping
public
private
static

3. Overview String as an Object String as an Array of Characters
Equalities
Length
Index
Substring

4. The Java String Class
Java String is the representation of a group of consecutive characters
Simplest String is a String Literal
String strGreeting = "Hello world!";
You can also create a String from an array of Characters
char[] strHelloArray = {'h','e','l','l','o','.'};
String strHelloString = new String(strHelloArray);
System.out.println(strHelloString);

5. Immutable Java String Class is immutable
Once created and initialized, cannot be changed on the same reference
The only way to change the value of immutable variables is to create a new object and point to that instead

6. Immutable String strCityName; // define the variable
Memory
String strCityName; // define the variable
strCityName = "Valencia";
System.out.println(strCityName);
strCityName = "London";
strCityName = "Madrid"; a L o n d V l e c i R m M r
Valencia
London
Madrid

7. Immutable By default variables are mutable
Can also be made immutable by declaring them final
The String class has a number of methods that appear to modify strings
Since strings are immutable, what these methods really do is create and return a new string that contains the result of the operation

8. What is the result of the comparison?
Equalities
A String may contain the same characters without being the same object
String str1stPersonsName = "John";
String str2ndPersonsName = "Peter";
String str3rdPersonsName = new String("John");
String str4rdPersonsName = str1stPersonsName;
What is the result of the comparison?
str1stPersonsName == str2ndPersonsName
str1stPersonsName == str3rdPersonsName
str2ndPersonsName == str3rdPersonsName
str1stPersonsName == str4thPersonsName
false
true

9. Equalities
Use the method equals(String) to compare the contents of two strings
Use operator == to see if both string objects are the same
Not that they contain the same group of characters but they are the same object

10. What is the result of the equalities?
String str1stPersonsName = "John";
String str2ndPersonsName = "Peter";
String str3rdPersonsName = new String("John");
String str4rdPersonsName = str1stPersonsName;
What is the result of the equalities?
str1stPersonsName.equal(str2ndPersonsName)
str1stPersonsName.equal(str3rdPersonsName)
str2ndPersonsName.equal(str3rdPersonsName)
str1stPersonsName.equal(str4thPersonsName)
false
true

11. Properties int length() char charAt(int)
Returns number of characters that compose the string
String str1stPersonsName = "John";
str1stPersonsName.length()
char charAt(int)
Returns the character at the specified position in the base string
str1stPersonsName.charAt(3)  4 
'c'

12. Searching Strings String substring(...) int indexof(...)
Return a sub-string of the base string
str1stPersonsName.subString(1, 2);
int indexof(...)
Returns the index where the specified string exists within the base string
str1stPersonsName.indexof("hn");
str1stPersonsName.indexof("hl"); 
"oh"
starting position
length  2  -1

13. Split
You can split up strings to get an array of strings using the split method
This uses a regular expression to break up a string
So you can create an array of words in a sentence by searching for the space character
HOWEVER a special character needs to be escaped with a "\" but since "\" is also a special character in Java, you need to escape it again with another "\" !
Any string in Java that uses any of the special characters like, “ \ must preceded by \ to escaped is special meaning and use it as character, e.g. "Valencia \"Spain\" Europe"

14. Split
String strCityNames = "Valencia London Madrid Rome"; String astrCityNames; astrCityNames = strCityNames.split(" "); System.out.println("Num cities " + astrCityNames.length()); for (String strCityName : astrCityNames) { System.out.println(strCityName ); } // end for
Num cities 4
Valencia
London
Madrid
Rome