Chapter 1 Helper Sheet

Java Template for introductory projects - just know how to use it when you have it for reference:

public class classname{

public static void main(String[] args) {

the program work is all in here
}

}

Types:

• no decimals: byte -> short -> integer -> long
• decimals: float -> double
• characters: char (and String, which is really a class of characters)
• yes/no: boolean

Create a variable:

type name ; OR type name = value; // (For String use " ", for char use ' ')

ex: int x = 1;

Change a variable:

variable = something; // something can be another variable or math using * / + -

ex: x = y * 2 / 3 + a;

Print to the screen:

System.out.println ( what you want to output ); // inside parentheses put "string" and variables separated with +

ex: System.out.println ("The average is" + avg + "\n The product is:" + product);

Play with strings:

• stringvar.charAt(3) // will be a character
• stringvar.length() // will be an integer
• stringvar.equals(somethingOtherString) // will be either true or false (a boolean)
• stringvar.toUpperCase() // will be a String that is all uppercase
• stringvar.toLowerCase() // will be a String that is all lowercase
• stringvar.subString(2) // will be a String starting in position 2 to the end
• stringvar.subString(2, 5) // will be a String starting in position 2 and ending in position 4

ex: newString = myOriginalString.toLowerCase();

Also, strings can be put together into another string with the +

ex: newString = string1 + string2;

Variable name (Identifier) rules:

• An identifier must begin with a letter or an underscore _
• Java is case sensitive upper case (capital) or lower case letters are considered different characters. Average, average and AVERAGE are three different identifiers.
• Numbers can also appear after the first character.
• Identifiers can be as long as you want but names that are too long usually are too cumbersome.
• Identifiers cannot be reserved words (special words like int, main, etc.)
• By convention, variables should begin with a lower case unless they are really representing something that wont ever change
• By convention, a variable whose value should never change should be all capitalized.

Comments:

• // -> comment line ex: // this is a comment
• /* xxx */ comment between marks