Download lect15 Final

What If?
• Write a program that prompts for the names
and locations of 1000 employees. Store the
information in the program for later use.
Program for Previous
String empName1, empName2, empName3,…
String empLocation1, empLocation2, …
System.out.print( “Enter employee name 1:”);
empName1 = scan.next();
System.out.print(“Enter employee name 2:”);
empName2 = scan.next();
…
//Can we use a loop?
Arrays
• Syntax:
type variableName[] = new type [size];
• Syntax:
type [ ] variableName = new type [size];
• Memory Is Set Aside for size Items of type
• Each Variable Location in Array Is Accessed by
Offsetting into the Array with an Integer Expression
• Legitimate Offsets Are 0 to size-1
Array Example
char [] lastname = new char[100];
lastname[0] = ‘H’;
lastname[1] = ‘a’;
lastname[2] = ‘\0’;
System.out.println( lastname[0]);
Array Example
int [] values = new int[15];
values[0] = 150;
values[1] = 78;
values[2] = 16;
System.out.println( values[0]);
values[3] = values[0] + 6;
Array Example
final int ARRAY_SIZE = 100;
int offset;
int [] numArray = new int [ARRAY_SIZE];
for(offset = 0; offset < ARRAY_SIZE; offset++)
{
numArray[offset] = 0;
}
for(offset = 0; offset < numArray.length;
offset++)
{
numArray[offset] = offset;
}
Array Example
final int ARRAY_SIZE = 10;
int offset, sum = 0, average;
int [] numArray = new int[ARRAY_SIZE];
for(offset = 0; offset < ARRAY_SIZE; offset++)
{
System.out.print( “Enter Score ” + offset + “ : “);
numArray[offset] = scan.nextInt();
}
for(offset = 0; offset < ARRAY_SIZE; offset++)
{
sum = sum + numArray[offset];
}
average = sum / ARRAY_SIZE;
Arrays of Objects
// The following does NOT create memory for
// objects, it only makes a blueprint array
Employee [] employees = new Employee [MAXEMP];
// Must create memory and call constructor for
// each single member of aray of objects
for (i = 0; i < MAXEMP; i++)
employees[i] = new Employee();
Passing Arrays to Methods
• Pass Array Name into Method
int [] intArray = new int[100];
loadArray(intArray);
• Accept into Method as an Array with No Set Size
void loadArray( int [] passedArray )
• Changes to Array in Method *will* Update
Original Array
public static void main(String [] args)
{
final int ASIZE = 5;
int [] intArray= new int[ASIZE];
for(int i = 0; i < ASIZE; i++)
intArray[i] = i;
System.out.println( intArray[0]);
changeZero(intArray);
System.out.println( intArray[0]);
}
static void changeZero(int [] passedArray)
{
passedArray[0] = 1000;
}
Initializing Arrays
char [] cArray3 = {'a', 'b', 'c'};
int [] iArray = {1, 2, 3, 4};
double [] dArray = {3.4, 5.67e4};
Two Dimensional Arrays
char [][] cArray = new char[10][20];
int [][] iArray = new int[100][50];
cArray[0][0] = ‘a’;
cArray[0][1] = ‘b’;
cArray[9][19] = ‘x’;
iArray[0][0] = 99;
iArray[1][5] = 135;
iArray[99][49] = 0;
Math Class
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Contains Typical Math Methods
In Package java.lang (i.e., automatically imported)
Access using Math.math_thing
Math.PI; Math.E (log e = 1)
double pow (double base, double exp)
double sqrt(double number)
int round(double number)
int abs( int number)
min(number1,number2) and max(number1, number2)
double random(); //random number between 0.0 and 1.0
Tokenizing/Parsing
• Taking Apart a String and Separating It into
Smaller Strings (i.e., “tokens”)
• Usually, Tokens are Items Separated by
Whitespace
• Tokens Can Be Defined with Different
Separators
• Parsing Takes Tokens and Applies Some
Manipulation of Those Tokens
StringTokenizer Class
import java.util.*;
…
String bigString = “This is a sentence.”;
StringTokenizer st = new
StringTokenizer(bigString);
while (st.hasMoreTokens())
{
System.out.println(st.nextToken());
}
// Displays This, is, a, and sentence. one
// per line
Static Variables and Methods
• static means “in class” methods and
variables
• static variable: one per class (not one per
object)
• static method: no invoking object (invoke
with className.method())
Static Variable Example
public class MyClass {
…
private final int STARTID = 1;
private int IDNum = -1;
//above are one per object
private static int nextIDNum = STARTID;
//above is one per class
public MyClass()
{
…
IDNum = nextIDNum;
nextIDNum++;
}
Static Method Example
public class MyClass {
…
private final int STARTID = 1;
private int IDNum = -1;
//above are one per object
private static int nextIDNum = STARTID;
//above is one per class
…
public static int GetNextID()
{
// Called by MyClass.GetNextID()
return nextIDNum;
Other Class Methods
• boolean equals( objType comObj)
– compares invoking object with parameter of same type.
Returns true if equal, false if not.
• void display()
– displays object to monitor
• String toString()
– converts each attirbute to String and returns String
Employee Class Review
• Create a Class Employee
• Employee.java
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Employee Attributes (data members)
Constructor
Accessor Methods
Mutator Methods
toString() and equals()
• tryEmployee.java (Client Test Program)
Final Exam
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2 Hours
200 Points
35% of Grade
Must Take to Pass Course
Need to Know for Final
• Everything Through Exam 2
• Plus:
– Arrays
– Methods
– Classes
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Constructors
Accessor Methods
Mutator Methods
toString() and equals() Methods
Final Exam
• 200 Points Total – 35% of Final Grade
• 90 points Matching or Short Answer or
Multiple Choice (Terminology, Operators,
JAVA Basics)
• 30 Points Program Output
• 80 Points Programming (Full Programs)