User:ddixon

From ggc

Notes

Study Guide - Test 2 1. Declare an array of integers called y.

int[] y;

2. Write a statement to initialize the integer array y to be able to hold 27 elements.

y =new int[27];

3. Write a loop to fill the array y with the even numbers from 20 to 126.

    for(int i = 0; i <= 53; i++)
          y[i]=20+2*i;

4. Given an array of integers called y, write a loop to print all of the integers to the console on separate lines.

for(int i = 0; i < y.length; i++)
{
    System.out.println("The number is " + y[i]);
}

5. Given an array of integers called y, print out all of the odd integers to the console.

for(int i = 0; i < y.length; i++)
{
    if(y[i]%2 != 0)	// y[i]%2 == 1
    {
        System.out.println("The number is " + y[i]);
    }
}

6. Write a method that changes each element in the array y to triple its original value.

for(int i = 0; i < y.length; i++)
{
    y[i]=3*y[i];
}

7. Which type of variable is known about most widely (has the largest scope): instance variable, local variable or parameter? instance variable

8. What is the difference between defining (writing the declaration and body) a method and calling (also known as invoking) a method?

9. When should you use arrays? ArrayLists?

ArrayList<Integer> x;
x=new ArrayList<Integer>();
for(int i=20; i<=126; i+=2)//increase i by 2, i=i+2
{
   x.add(i);
}

for(int i=0; i<x.size(); i++)
{
  if(x.get(i)%2==1)
  {
      System.out.println(x.get(i));
  }
}
for(int i=20; i<=126; i+=2)//increase i by 2, i=i+2
{
   x.add(i);
}

10. What is a plain English description of what the following loop does? for(int i=0; i<y.length; i++) { if(y[i]>0) System.out.println(y[i]); }

10110=1*16 + 0*8 + 1*4 + 1*2 + 0*1 = 16+0+4+2+0=22

10110.11=1*16 + 0*8 + 1*4 +1*2 + 0*1 + 1*1/2 +1*1/4= 22.75

22 % 2 = 0
11 % 2 = 1
5  % 2 = 1
2  % 2 = 0
1  % 2 = 1
0  % 2 = 0
0  % 2 = 0
0  % 2 = 0
00010110 = 10110

0.625 * 2 = 1.25
0.25  * 2 = 0.5
0.5   * 2 = 1.0
0     * 2 = 0.0
0     * 2 = 0.0

0.625=0.101000000

300=300
000300 = 300

variable a storaqge location in the computer's memory that has a type, aname and a contents.

 Example: String greeting = "Hello, World!"; greeting is the variable.lowerUpper

method-contains a collection of programming instructions that tell how to carry out a task.

 Example: System.out.println("Hello, World!"); println is a method

class-defines the methods that you can apply to its objects

 Example: public class HelloPrinter , HelloPrinter is a class UpperUpper

constructor-is a method that initializes a newly instantiated object.

 Example: Rectangle box = new Rectangle (5, 10, 20, 30); Constructs a Rectangle

parameter-is an input to a method

 Example:System.out.println; (greeting); (greeting) is a parameter

return value-a result that the method has computed for use by the code that called it.

 Example: int n=greeting.length(); returns a value

object-a value of a class type

 Example: System.out.println; ("Hello, World!"); ("Hello, World!") is an object that belongs to the String class

instance field-variable defined in a class for which every object of the class has it's own value (values are unique to each instance of a class)

 Example: balance variable of BankAccount class

local variable-variable whose scope is a block, only visible to methods where the are declared and are not accessible from the rest of the class.

 Example: newBalance of the deposit method

implicit parameter-is the object on which the method is invoked

 Example: System.out.println; ("Hello, World!"); System.out is the implicit parameter.

explicit parameter-a parameter of a method other than the object on which the method is invoked.

 Example: System.out.println; (greeting); (greeting) is an explicit parameter

declare-Specifies name and type

 Example: Rectangle rectangle; Where Rectangle in the type and rectangle is the name.

initialize-setting a variable to a well-defined value when it is created.

 Example: rectangle = new Rectangle (10, 10, 20, 30); (10, 10, 20, 30) gives   height,         width,(x and y= location)

type-a named set of values and operations that can be carried out with them.

 Example: ("Hello, World!") has the type String.

access specifier- A keyword that indicates the accessibility of a feature.

 Example: public class BankAccount public is the access specifier.

"2" a string converted in a string bond from and integer to string 2 is an integer however it can be converted into a string as in a String bond, '2' is a Character constant as seen in appendix B "2.0" a string converted in a string bond from and integer to string 2.0 is an double type integer

 public, class, private, import, package 			           keyword
 /**
 * All about my class here.
 * @author Jam Jenkins
 */ 			                                                    comment
 public class HelloGame extends GameLoop			  class declaration
 private Sprite hello;			    instance variable declaration (field declaration)
 public void startGame()			                 method declaration
 hello=new StringSprite("Hello World");			     initialization
 hello.setLocation(0.5, 0.5);
 and 
 canvas.addSprite(hello);			calling a method (invoking a method)
 hello			                                                  argument
 {
    private Sprite hello;
    public void startGame()
    {
       hello=new StringSprite("Hello World");
       hello.setLocation(0.5,0.5);
       canvas.addSprite(hello);
    }
 } 			                                                class body
    {
       hello=new StringSprite("Hello World");
       hello.setLocation(0.5,0.5);
       canvas.addSprite(hello);
  } 			                                                method bocy
 Jam, fang, HelloGame, GameLoop, hello, StringSprite 			identifier

The for Statement

 for (initialization; condition; update)
     statement

 Purpose: TO execute an initialization, then keep executing a statement ans updating an expression while a condition is true.i=iterations

debugger is a program that you can use to execute another program and analyze its run-time behavior Array

 1.an Array is a sequence of values of the same type
 2. how to construct an Array with 10 floating point number: new double [10]
 3. declarion of an array variable: double[] data = new double[10] That is, data is a   ference to an array

4. Two-D arrays form tabular, 2d arrangement. You can access elements with an index paira [i][j].

LENGTH use the length field to find the number in an array ArrayList

 1. manages a sequence of objects
 2. --ArrayList caqn grow and shrink as needed
 3. the arraylist class supplies methods for many common tasdks, such as inserting and   moving elements
 4. to get objects out of the arraylist use the get method, not the [] operator

return statment

return expression; or return; Example return balance; Purpose to specify the value that a   method returns, and exit the method immediately. The return value of the method call   expression.