1. String Input ICS 111: Introduction to Computer Science I
William Albritton
Information and Computer Sciences Department at the University of Hawai‘i at Mānoa
“If you study to remember, you will forget, but if you study to understand, you will remember.”
Unknown
11/18/2018
© 2007 William Albritton

2. Input Problem
Your friends are so impressed that their friends now want a program that displays their name in all lowercase & uppercase
Understand the problem
You are getting tired of rewriting programs, so you just want one program that can be used by anyone
Write an algorithm
Ask the user to enter name & store the name
Print name in all lowercase & uppercase
Write the computer program
See InputName.java
11/18/2018
© 2007 William Albritton

3. Output in Java What is System.out?
An automatically created object that represents output to the monitor (screen, console)
out is an object located within the System class
out is an object of PrintStream class
Sends a stream of data to the console window
See Java API for class System, and look under “Field Summary” for object out
Terminology
The term “I/O” is short for “Input and Output”
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© 2007 William Albritton

4. Output in Java Class PrintStream 3 common methods of class PrintStream
System.out.print("Aloha!"); //Aloha!
System.out.println(); //newline
System.out.println("Ossu!"); //Ossu! + newline
See Java API for class PrintStream
11/18/2018
© 2007 William Albritton

5. Input in Java What is System.in?
An automatically created object that represents input from the monitor (screen, console)
in is an object located within the System class
in is an object of InputStream class
Receives a stream of data from the keyboard
Cannot use System.in directly
Have to use an object of the Scanner class to do input
See Java API for class System, and look under “Field Summary” for object in and class InputStream
11/18/2018
© 2007 William Albritton

6. Class Scanner
Class Scanner organizes the “raw” stream of data from the keyboard into more manageable units such as a String object
To use a Scanner object
Put import statement at top of file
import java.util.Scanner;
Create a Scanner object
Scanner keyboard = new Scanner(System.in);
Get one full line of input & store as a string
String line = keyboard.nextLine();
11/18/2018
© 2007 William Albritton

7. Scanner Methods
nextLine() returns everything that was typed on a single line on the console
All typed input until user presses “Enter” key
These characters are stored in a String object
next() returns the first word (also called a “token”) typed on a single line on the console
All characters up to the next blank space (a space, newline, or tab)
11/18/2018
© 2007 William Albritton

8. Escape Sequence How can we output quotations within a string?
Use special characters that begin with a backslash character (\)
double_quote = \"
single_quote = \'
newline = \n
tab = \t
backslash = \\
System.out.println("She said \"Hello\""); //She said "Hello"
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9. Class Exercise 1
Write a Java program that prompts the user to enter their first & last names. Display the user’s initials.
Two choices for user input:
Ask the user to enter the names separately & use Scanner method nextLine()
Ask the user to enter BOTH names at once, & use the Scanner method next(), which returns all characters up to the next blank space (a space, newline, or tab)
11/18/2018
© 2007 William Albritton

10. A Fourth Step
“The best laid plans of mice and men often go astray” – John Steinbeck, Of Mice & Men
Often, your day does not go as planned
May fall asleep on the train & miss correct stop
May get lost underwater while scuba diving
May forget something when taking a friend surfing
We need to add a 4th step to problem solving
Understand the problem
Make a plan (algorithm)
Implement the plan (computer program)
Fix/redo/improve the plan (debugging)
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© 2007 William Albritton

11. Address Problem
Let’s prompt the user for first & last name, and output their address
Algorithm
Ask the user for first & last name & store separately
Store the first letter of first name
Store the first 7 letters of last name
Add the first two strings and
Output the address
Computer program
See .java
11/18/2018
© 2007 William Albritton

12. Debugging The Email.java program has lots of bugs!
Where does the term “bug” originate?
See “links” column on webpage for details
So where do we start with debugging a program?
Trace through the code in our heads
1st step to debugging, but often cannot see past our own “logic”
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© 2007 William Albritton

13. Debugging What is another way to debug a program?
Put lots of System.out.println() statements in code to get feedback
System.out.println("variable:" variable);
But must do a lot of typing…
Use a Debugger
A function of an IDE (Integrated Development Environment) that helps you to “step through” a program
For detailed instructions, see jGRASP debugger tutorial under the links column
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© 2007 William Albritton

14. Using the Debugger Steps to using the debugger
Position mouse on the left side of the program window, somewhere within the main() method
A red dot should appear
Click on the red dot
The red dot should become permanent
Compile the program
Click on the Ladybug icon
This will “Run debugger on current file”
Press top left blue arrow to step through code
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© 2007 William Albritton

15. Class Exercise 2 Identify the bugs & fix them See Email.java
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© 2007 William Albritton

16. String Methods replace(target, replacement)
Replaces target string with replacement string
See program ReplaceExample.java
String string1 = new String("abcd"); String string2 = string1.replace("bc", "HEA"); System.out.println(string1); //abcd System.out.println(string2); //aHEAd
Note that String methods do not change the original string
String methods return a different string
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17. String Methods substring(start, end) substring(start)
Returns a substring made up of the characters from start to end-1 in the original string
String string = new String("abcde");
System.out.println( string.substring(1,3));//output "bc"
substring(start)
Returns a substring made up of the characters from start to the ending of the string
System.out.println( string.substring(2));//output "cde"
11/18/2018
© 2007 William Albritton

18. Class Exercise 3
Write a Java program that asks the user to enter a sentence, then replace all the blank spaces in the sentence with the word “BLANK”
For example, “This is a pen.” would change to “ThisBLANKisBLANKaBLANKpen.”
11/18/2018
© 2007 William Albritton