• Create a new program

public class MyClassName
{
     // you can define a class variable here
     public static void main( )
     {
           // your statements will go here
           // your calls to method1 will have the form: method1()
     }
     public static void method1( )
     {
           // your statements will go here
     }
}

• create a variable
  • In Java: <type> <variable name> ;  example: int myIntVar;
  • declare with correct type: int, double, char, boolean, (not capitalized)
  • declare Object variables with types such as : String, Scanner, Random, (capitalized)

   

• change variable contents:
  • In Java: <variable name> = <some expression>; example:  myIntVar = 5 ;.

• Say something on the screen: 
  • In Java: System.out.println(<whatever you want to print> + <whatever you want to print> );
    
  • example: System.out.println("Hello, my name is " + myName + "My number is " + myNumber);
  • Remember: the semi-colon; capitalize System, use both parentheses;
    
  • Remember quotes around text and not around variable names
  • variations: printf and print

• Work with methods
  • Define a method
    • add a method right before the class closing curly braces
    • a method header is immediately before the method's curly braces
      • ex: public static double myMethod(int x){ // your statements go here}
    • a method's parameter variables are created inside the parentheses (ex: in the statement above, int x is the parameter creation
    • a method's return type is defined before the method name (ex: in the statement above, double is the return type)
    • a method with a return type needs to end with a return statement.
    • a method with no return type (void) cannot have a return statement
  • Call a method:
  • for static methods you create: <method name> (any parms). ex: myMethod(3);
  • for static methods that are not in your class: <class>.<method name> (any parms) ex: Math.pow(5,2);
  • for instance methods that are not in your class: <object>.<method name> (any parms) ex: myScanner.nextDouble();
  • parameters must match in type and number
  • for methods that return a variable: set it = to something. ex: myDoubleVar = myMethod(3);

• Create boolean expressions:
  
  • use when you want to save the result of a true/false question
  • use comparison operator: ==, <,>,<=,>=,!=
  • use logical indicator
    • OR is ||
    • AND is &&
  • example: myBooleanVar = x > 5 && x < 10 (x can be between 5 and 10)
  • example: myBooleanVar2 = x <5 || x >10 (x can be less than 5 or greater than 10)

• Setup to read something from the screen:
  • In Java: there are 2 commands needed:
    
  • before the class starts, import the scanner class using: import java.util.Scanner;
  • inside the method, create a scanner object using: Scanner kbd = new Scanner(System.in);
    
  • In Alice: Not needed, but similar to importing a character using file / import

   

• Read something from the screen:
  • In Java: <your variable> = < name of the scanner you created above>.nextLine();
    
  • Ask the user for something first, or the system will appear to hang waiting for the user to answer a question you never asked.
  • Use the scanner method that matches your variable type.
  • example to get the whole line: myStringVar = kbd.nextLine();
  • example to get the next word: myStringVar = kbd.next();
  • example to get the next double: mydoubleVar = kbd.nextDouble();
  • example to get the next int: myIntVar = kbd.nextInt();
  • See Sun's page on scanner for much more
    
  • In Alice: Drag the variable down to create a set command and drag over the world's "Ask user for a number" function.

You need to know how to use these for the midterm, but you do not need to memorize the commands. If you are asked to call these methods, you will be given the method name and parameters.

• Math
  • absolute value ex: myDoubleVar= Math.abs(#);
  • random ex: myDoubleVar = Math.random();
  • minimum: Math.min(#,#)
  • maximum: Math.max(#,#)
  • raise to a power: Math.pow(#,#) : Note: The first number is raised to the second number
    
  • knows PI and E
    

• Strings
  • stringvar.charAt(3) // will return a character
  • stringvar.length() // will return an integer
  • stringvar.toUpperCase() // will return a String that is all uppercase
  • stringvar.toLowerCase() // will return a String that is all lowercase
  • stringvar.subString(2) // will return a String starting in position 2 to the end
  • stringvar.subString(2, 5) // will return a String starting in position 2 and ending in position 4
  • stringvar.equals(someOtherString) // will return either true or false (a boolean)
  • stringvar.indexOf(someOtherString) // will return either the index of the location or -1 to indicate not found
    

  • ex: newString = myOriginalString.toLowerCase();

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

    ex: newString = string1 + string2;

Creating methods:

public static return_type method_name (type parm1, type parm2)
{
...
...
return expression;
}

Calling methods:

object_or_class.method_name(parm1, parm2);

• You need the class or object if the method is not in your own class.
• Then, you need the object if the method needs to know some information that is not passed in.

  Class with methods creation step by step guide

If / if else / else

if (condition that evaluates to true or false)
{
// do something
}
else if (condition that evaluates to true or false) // remember that everything that met first criteria doesn't get here
{
// do something else
}
.
. // repeat else if as needed
.
else // remember to put no condition
{
// do something
}

If facts:

• else is not needed
• when the condition is met, it executes inside the parentheses and then goes to the end of the if and continues on down
• You can have ifs inside the brackets for another if

Loops

For loop - repeats when you know the number of times to repeat

for (statement to start the loop; condition that evaluates to true or false; statement to run when the loop repeats)
{
// do something
}

For facts:

• Don't put a semi-colon at the end of the for condition
• Remember to create the variable used to count the loop with an int statement somewhere in your program. (either in the for statement or before it)
• You can add to the counter between the brackets as well.
• After the first time through, the for loop does the "statement to run when the loop repeats" first, and then checks whether the condition fails.
• When the condition fails, it goes to the bottom bracket of the loop and continues on
• You can have loops inside loops
• Stopping when equal to a single number is dangerous - go with < or > instead when you can.

While loop - repeats until some condition is met

while (condition that evaluates to true or false)
{
// do something
// at some point, set the condition to stop
}

• Don't put a semi-colon at the end of the while condition
• Remember to have something inside your loop that will make the condition fail sometime, or it will NEVER END
• When the condition fails, it goes to the bottom bracket of the loop and continues on
• The condition is only checked when it gets to the bottom bracket. Reaching the bottom bracket causes it to go back up to the top and check
• You can have loops inside loops