Transcript Extra Notes Lab #2

Martin T. Press
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Main Method and Class Name
Printing To Screen
Scanner
The main method is the starting point of execution of the Java program. Without
a main Method a Class is not runnable by itself. A Java project must have at least
one class with a main. Most of the first few labs will have one class .
The parameters Of the method: The Main Method Away takes a list of type String
The Return Type : always void (means returns nothing)
Remember always include public static at the beginning of the method. If this is
left out the complier will not recognize it as the “main”.
Every .java file written must have a class name. It must be the same name as the
.java file . Failure to name it the same as the file name will cause a compile error.
Class Name Sum
The Public Key word tells the
complier that all classes can
see it! I
File Name Sum.java
The System.out.print() and System.out.println() will be the only visual output for the first
few labs. It displays text that is inside the ( ).
The + operator when used with strings pushes
them together. Such that “Hello ”+5 is the same
as the String “Hello 5”. This is useful when
printing!
Scanner Is the object that allows programs to get Input data from the user on the command
line. The two methods we will use in this lab are nextDouble() and nextInt()
This is the import statement which tells the complier where the Scanner object is located in the
java library. You must always include this when scanner is used.
This is a constructor for the Scanner (creates the object).
It always takes System.in as a parameter for reading the command line.
myScanner.nextDouble()
Returns the next double entered by
the user(Waits till user hits enter).
This is the output from the previous example of code. Notice that even if an integer is
entered the output is still a double for the double. Try it the other way around what
happens?
Looks like an error occurred. Last time it worked because of type casting. A good rule of
thumb is if the scanner is expecting a type to always input the same type.