INTRO TO JAVA (PART 3) -
WRITTEN BY: M.WORTHINGTON [01.02.02]
...after checking out the first two tutorials you should you
should now be able to make a running program as well as mess around with numbers. now it
is time to endulge ourselves in the world of strings.
in our class StringsAndThings we will be using the variable type: String. the 's' must
always be capitalized in the word 'String'. a String is any type of text. it can be
letters, symbols, and even numbers. however, if the variable is defined as a String and it
has a value of a number, it will not functino like a number, it will not function like an
int or double. to explain, look at the following:
String a = "1"; //correct
String a = 1; //incorrect
int a = "1"; //incorrect
int a = 1; //correct
String b = "2";
String c = a + b;
if you print out c, you would get 12 (1 and 2 is 12 in string format). c
would not be 3 (1 + 2 = 3).
a key thing to know about Strings is that each letter or character of the string has an
index. the indexes of a string go from 0 to the length of the string minus one. for
example:
String k = "Funky Town";
Funky Town
0123456789
The index of F is 0
The index of u is 1
The index of n is 2
The index of k is 3
The index of y is 4
The index of is 5
The index of T is 6
The index of o is 7
The index of w is 8
The index of n is 9
The length of this string is 10, but as you can see, the last index is 9 (the length minus
one). Always remember that the index starts at 0.
in this program, StringsAndThings we will be using string variables and some of their
functions. they are as follows:
.length() <--- produces an integer of the length of the string
.substring(beginning position, ending position) <---prints out a specified part of the
string
.toUpperCase() <---PUTS ALL OF THE CHARACTERS IN THE STRING TO UPPER CASE
.toLowerCase() <---puts all of the characters in the string to lower case
OBJECTIVE
to create, use, and manipulate Strings. this tutorial doesn't contain all of the useful
functions that come along with Strings, but it does have the basics. i figured i'd get
these out first for you to soak up, and i'll introduce others in another tutorial.
PROGRAM
public class StringsAndThings
{
public static void main(String[] args)
{
String first = "John";
String last = "Doe";
String full = (first + " " + last);
System.out.println("first name: " + first); // Line 1
System.out.println("last name: " + last); // Line 2
System.out.println("full name: " + full); // Line 3
//length
System.out.println("first name has " + first.length() + "
characters"); // Line 4
System.out.println("last name has " + last.length() + "
characters"); // Line 5
//substring
System.out.println("last, first: " + full.substring(4,8) + ",
" + full.substring(0,5)); //Line 6
System.out.println("last, first: " + full.substring(4) + ",
" + full.substring(0,5)); // Line 7
//upper, lower cases
System.out.println("first name: " + first.toUpperCase()); // Line 8
System.out.println("first name: " + first); // Line 9
first = first.toUpperCase();
System.out.println("first name: " + first); // Line 10
System.out.println("first name: " + first.toLowerCase()); // Line
11
System.out.println("first name: " + first); // Line 12
first = first.toLowerCase();
System.out.println("first name: " + first); // Line 13
} //main
} //class
ABOUT THE PROGRAM
on each line of coding that is going to print something out is a comment that has an
assigned number line. this is just so referring to each line will be easier to understand.
OUTPUT
be sure to compile the program and then run it. refer back to the first tutorial for
instructions.
the following is output from each line(minus the line reference) as you should have
when you run the program:
Line 1: first name: John
Line 2: last name: Doe
Line 3: full name: John Doe
Line 4: first name has 4 characters
Line 5: last name has 3 characters
Line 6: last, first: Doe, John
Line 7: last, first: Doe, John
Line 8: first name: JOHN
Line 9: first name: John
Line 10: first name: JOHN
Line 11: first name: john
Line 12: first name: JOHN
Line 13: first name: john
EXPLANATION
first, i want to jump straight to the upper and lower case section. while lines 8 and 11
printed out the first name in Upper and Lower Cases, respectively, they did not change
what the variable itself contained. the contents of the variable do not change until after
lines 9 and 12. lines 1 through 3 simply print out the contents of the variables. lines 4
and 5 simply print out the length of the strings. lines 6 and 7 print out substrings. line
6 prints out the characters at the 4th, 5th, 6th, and 7th indexes in the string, but not
the 8th. the substring ends at the 8th index but does not include it. it then prints out the comma and the characters from 0 to 4, but not including the character with the index of 4. the only difference between lines 6 and 7 is that the first substring only has one number in the parenthesis. putting only one number in the substring parenthesis means 'print from this spot to the end of the string.' it is as simple as that. i suggest messing around with substrings until you completely have a grasp on them. they're not difficult,
but simple mistakes with them will annoy you later down the road.
if you're still having trouble with the program and understanding it, your best bet is
to just mess around with it. change up the variables, variable types (include ints and
doubles in the program), values, and functions; before running the program, try to
predict what is going to be printed out.
any other questions, hit up the message
boards. if you chat there you can easily go ahead of tutorials and learn more
programming.
please let me know what you think of this tutorial by going to the message boards or the contact page to submit your
comments. thank you.
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