1. Strings
A String is a sequence of letters
In Java, strings are contained in an object that is an instance of the String class.
String in java is the name of a class. That’s why it starts with a capital. It is NOT a reserved word.
The String class has lots of useful methods.
You can look these up at:

2. To declare a string The way we’ve seen before: String str = "abcdef";
A new way: String str = new String("abcdef");
Notes:
In Java the reserved word new instantiates (creates) and instance of a new object following the blueprint that its class defines
In the above example str contains an object of type string.
To put a string into str, we can say things like: str = "abc"; or str = IO.readString();

3. Comparing Objects
Primitive variable types: byte, short, int, long, float, double, char, boolean
Object variable types: thoes created from a class like String
Object variables and string variables store differently in memory
Objects to be compared must contain an equals method
str1 == str2 compares memory addresses, not contents
str1.equals(str2) compares contents x 23
Primitive variable
Example: int x = 23;
Address of "abc
str
"abc"
Object Variable
Example: String str = "abc";
null
Object Variable with nothing in it.
Example: String str;
str

4. String Methods
str.trim() eliminates leading and trailing spaces from String, str.
str.length() returns the number of characters in the String, str
str.substring(x,y) returns the String starting at the x position up to but not including the y position of String, str.
str.replace(oldChar, newChar) replaces all occurrences of oldChar by newChar in String, str
str.charAt(x) returns the character at position x of String, str
Str.indexOf(‘x’,y) returns the first index to where ‘x’ appears in the String, str, starting from position y
str.toUpperCase() and str.toLowerCase() changes the case of a String str

5. String Method Examples
String s = " abcdefg ".trim() puts "abcdefg" into s
int i = "apple jack".length() puts a 10 into i
String s = "abcdef".substring(2,4); puts "cd" into s
String s = "abracadabra".replace(‘a’,’b’); puts "bbrbcbdbrb" into s
char c = "abcdefg".charAt(4); puts a ‘e’ into c
int i = "abracadabra".indexOf(‘a’,4); puts a 5 into i.
int i = "abracadabra".indexOf(‘e’,0); puts a -1 into i
String s = "abcdef".toUpperCase(); puts "ABCDEF" into s
Int i = "aeiouAEIOU’.indexOf(c); returns >=0 if c is a vowel.

6. Common Examples
We want to do a loop until the user enters either a "q" or "Q" Solution: while (value.indexOf("qQ")<0) { … }
We want to capitalize the first letter of a string and lower case the rest Solution: value = value.substring(0,1).toUpperCase() value.substring(1).toLowerCase();
We want to remove the space characters from a string Solution: value = value.replaceAll("\\s+", "");

7. Lab Hints Make the first letter of a string capital
Use the charAt() method to get the first letter
Strings are immutable; therefore str.charAt(0) = "A"; will not work
str.substring(0,1).toUpperCase() will work as long as the string has at least one character.
To find the second name of: "first middle last"
Use indexOf to find the spaces before
Use substring and trim to get "last middle" and eliminate leading and trailing spaces
If no more spaces, then the form is "first last" not "first middle last"

8. Review Questions
What is the difference between and object and a primitive variable?
How do you find out information about the many classes provided by Java?
String objects are immutable. What does this mean?
What is String concatenation?
Describe the use of the following methods:
Replace()
charAt()
indexOf()
toUpperCase() and toLowerCase()
trim()
How do you find the length of a string?
What is the index of the first character of a string?