Arrays. Exam 1 1. Java source and executable files have the following extensions? a..java and.class...

Arrays

Exam 1

1. Java source and executable files have the following extensions?

a. .java and .class

b. .src and .class

c. .javadoc and .exe

d. .list and .exe

Exam 1

2. Which of the following is a Java comment

a. ; This is my first program

b. # This is my first program

c. /* This is my first program */

d. ‘ This is my first program

e. none of the above

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3. We use the following operator to create a new object in Java

a. malloc

b. new

c. string

d. newObject

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4. Commands to compile and execute a java program are

a. run and java

b. execute and javac

c. javac and java

d. compile and run

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5. Identifiers may start with

a. $

b. @

c. a number

d. &

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6. It is necessary to declare an object before you can use it

a. True

b. False

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7. Which of the following is a valid identifier?

a. Bank Account

b. bank account

c. bank$account

d. bank-account

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8. A series of characters that appear in double quote is a char data type

a. True

b. False

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9. boolean isDone == false; is a valid assignment statement in Java

a. True

b. False

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10. Which of the following is a correct variable declaration statement?

a. int x - float y;

b. int x: float y;

c. int x,y;

d. Long int x;

Exam 1

11. Boolean expressions are built by use of _relational______operators and _boolean_______operators

12. A data value that can not be changed is called __constant____________

13. $Bad-Variable is __bad/invalid/not _ Java identifier.

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14. These two data types: __float__, and ___double___are used for real numbers

15. _An object____is an instance of a class

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16. double loanPeriod;

if (loanPeriod < 0 || >1000 ); {

System.out.println(“Loan period is invalid”);

System.exit(1);

}

1. loanPeriod is not initialized

2. loanPeriod or a variable name is missing

3. ; is not needed.

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17. double s;s = 1.0;switch (s) {case 1.0: System.out.println(“ March madness”); break;case 2.0: System.out.println(“ November rain”); break;case 3.0: System.out.println(“White Christmas”); break;default: System.out.println(“No Special name”); break;}

1. Switch doesn’t support double data type

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18. char aChar = ”NFL Championship”;

1. Char datatype can only contain 1 character

2. Char data type needs single quotes instead of double ones

Exam 1

19. int i, j;double x,y;i=1;j=2;x= Math.pow(3, (i/j)); y = x % 2;if (y ==0)System.out.println(x +" is an even number ");elseSystem.out.println(x +" is an odd number");

½ = 0, 30=1.0

y = 1.0 % 2 = 1.0

1.0 is an odd number

Exam 1

20. int count=1, sum=0;

while (count < 9) {

if (count % 2 != 0) {

sum += count;

}

count++;

}

System.out.println(" Sum ="+ sum);

Exam 1

count =1, sum =0, 1 %2 = 1 (!= 0), sum = 0+1=1count =2, sum=1, 2 % 2 = 0count =3, sum=1, 3 % 2 = 1 (!=0), sum = 1+3 = 4count =4, sum=4, 4 % 2 = 0count =5, sum=4, 5 % 2 = 1 (!=0), sum = 4+5 = 9count =6, sum=9, 6 % 2 = 0count =7, sum=7, 7 % 2 = 1 (!=0), sum = 9+7 = 16count =8, sum=16, 8 % 2 = 0count =9, exit

Sum = 16

Exam 1

21. int sum =0;

for (int i=1; i<=2; i++) {

for (int j=1; j<=3; j++) {

sum = sum + (i+j);

}

}

System.out.println(" Sum ="+ sum);

Exam 1

sum =0i=1;

j=1; sum=0+(1+1)j=2; sum =(1+1)+(1+2)j=3; sum = (1+1)+(1+2)+(1+3) = 2+3+4=9

i=2j=1; sum=9+(2+1)j=2; sum=9+(2+1)+(2+2)j=3; sum=9+(2+1)+(2+2)+(2+3)= 9+(3+4+5)=9+12=21

Sum =21

Lesson plan

Arrays

Arrays

We often need to group together related items of data.Cards in a pack.Ships in a port.

Java provides two distinct facilities:Traditional array.Flexible-size collection classes

(java.util).

Problems That Arrays Solve

……

minValue = firstNumber;if (secondNumber < minValue)

minValue = secondNumber;if (thirdNumber < minValue)

minValue = thirdNumber;if (fourthNumber < minValue)

minValue = fourthNumber;if (fifthNumber < minValue)

minValue = fifNumber;

……

What is this code doing?

Finding minimum value from a set of 5 values

Arrays for Numerical data type (primitive data types)

int[] number = new int [5];int minValue;

String inputStr;for (int i=0; i<5; i++) {

inputStr = JOptionPane.showInputDialog(null,"Please enter the value for element "+i);

number[i] = Integer.parseInt(inputStr);}

minValue = number[0];for (int i=1; i<5; i++) {

if (minValue > number[i])minValue = number[i];

}System.out.println(" minValue ="+ minValue);

Array declaration &

allocation memory









Getting values for all elements

in the array









Access each element of an

array

Arrays

Array is a collection of data values of the same data type.

Example:int[ ] number; // This is an array of integersdouble[] gpa; // This an array of double

Array Declaration

Format:<data type>[] <array_name>;

OR<data type> <array_name>[];

data type: double, int, float, stringExample:

double[] gpa;Or

double gpa[];

Arrays

The amount of memory allocated to store an array depends on the size and type of values in the array Size: number of elements in the array Type of values: data type of each element in the array An individual value in an array is called array element

Example:int[ ] number = new int[5];data type: integer (4 bytes)size: 5memory: 20 bytes

Array is a reference data type. Array is NOT an object

Arrays

Example:

int[ ] number = new int[5];

number

1 2 30 4

number[0]

6

Arrays

Elements of an array are indexed from zero to size -1

Size: the number of elements in an array length: a public constant represents the size of

an array.Example:

sum =0;for (int i=0; i<number.length; i++)

sum += number[i];

Fixed –size array declaration

Size of an array is pre-determined.Example:int[] number= new int[5];

Problems:• What if we have more than pre-

determined size of an array?• Underutilization of space.

Variable-size array declaration

In Java, we can declare an array of different size every time we run a program

Example:int size;int[] number;

inputStr = JOptionPane.showInputDialog(null,"Please enter the number of elements ");size = Integer.parseInt(inputStr);

number = new int[size];

Practice (in class and/or at home)

Modify the class ComputeMin (week 4) to print out the minimum of an array with n integers.

Arrays for Objects

// An array for the names of the distinct private Loan[] loanArray = new Loan[5];

• Note: No Loan objects are created. Only a container for Loan.

• Each location is initialized to null.loanArray

NULL

Arrays of Objects

private Loan[] loanArray = new Loan[5];

for (i=0; i<5; i++) {

loanArray[i] = new Loan();

}

loanArray

Indexing an Array

int[] number = new int [5];

number[0] =2;

number[1]=3;

number[2]=4;

number[3]= 6;

number[4]=-1;

Initializing Arrays

... // Differentially number the assignments. private int[] number = {1, 2, 1, 5, 1,}; private final int totalNumber = number.length;

• No new required.• Terminating semicolon.• Optional final comma.

Further Initializer Examples

String[] suitNames = { "Spades", "Hearts", "Diamonds", "Clubs"};

Point[] vertices = { new Point(0,0), new Point(0,1), new Point(1,1), new Point(1,0),};

YearlyRainfall y2k = new YearlyRainfall( new int[]{10,10,8,8,6,4,4,0,4,4,7,10,});

Note for project 2

a. For each class (Loan and Amortization), list:data members:

data type, namemethods:

return data type, name, parametersconstructor

parameters

Note for project 2

b. For Amorization main list

methods:

return data type, name, parameters

Draw a diagram

c. Submit your code

Test case

Interest rate = 0.4% (0.004)

Number of months = 12

Loan amount = 100

Amortization payment = $8.55

Iterating over an Array in Reverse

int size = 5;minValue = number[size-1];for (int i=size-2; i>=0; i--) {


}

Copy an array

Use arraycopy method from System class.

public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

Copying Arrays

int size=5;int number[] = new int[size];

// Assuming that we get values for number array here

// Declare another array called number1 int number1[] = new int[size];

// Copy the values of array number to array number1System.arraycopy(number,0,number1,0,size);

Passing Array to Methods

When an array is passed to a method, only its reference is passed. A copy of the array is not created in the method.

That means:

we pass the identifier for that array which in fact is a reference to a start address of the array.


Assuming changeArrayValue is one method of a class named ArrayClass

public void changeArrayValue(int[] arrayChanged) {for (int i=0; i< arrayChanged.length; i++)

arrayChanged[i] += 1;

}

We call this method as:


ArrayClass anObj = new ArrayClass();

int number[5] = new int[5];

for(int i=0; i<number.length; i++)

number[i] = i;

anObj.changeArrayValue(number);


for(int i=0; i<number.length; i++)

number[0] = i;

anObj.changeArrayValue(number);

0 1 2 3 4

1 2 3 4 5

number

number

“Just in time” overview

1. It is acceptable to have an array containing values of both type BYTE and type INT, as long as all of the values are integers:

a. True

b. False

“Just in time” overview

2. A code fragment that declares an array of type long named accounts is

a. long accounts;

b. long[ ] accounts;

c. long{ } accounts;

Matching game (again)

3. A code fragment that declares an array named grades and allocates the memory to store 15 values of type double:

= ;

A.[15] B. new C. gradesD. double E. double[ ]

Matching game (again)

4. A code fragment that declares an array named grades and allocates the memory to store 15 values of type double:

= ;

A.[15] B. new C. gradesD. double E. double[ ]

E BC D A

Searching an Unsorted Array

We often need to search an array for a particular item of data.

The data is often unsorted.The item might or might not be present.

Care must be taken not to search beyond the end of the array.

We need to decide how to return a found item.

Search with Multiple Returns

public int indexOf(int[] numbers,int value){ final int notPresent = -1; for(int index = 0; index < numbers.length; index++){ if(numbers[index] == value){ return index; } } // We did not find it. return notPresent;}

The Arrays Class

Defined in the java.util package.Contains static methods for manipulating

arrays:binarySearch: search for a value.equals: compare the contents of two

arrays.fill: fill an array with a particular value.sort: sort the contents of an array.

Multi-Dimensional Arrays

Arrays of multiple dimensions are possible.2D grid, for a board game such as chess.3D cube structure, etc.

Multi-dimensional arrays are regarded as being arrays of arrays.

Non-rectangular structures are possible.

2D Array Construction

final int numRows = 10, numCols = 5;double[][] matrix = new double[numRows][numCols];

char[][] hiddenWord = { { 'd', 'g', 'i', 'b' }, { 'e', 'i', 'u', 'm' }, { 't', 'a', 's', 'a' },};

Review

Arrays make it possible to group related items in a single object.

An array's length is fixed on construction.Arrays may have multiple dimensions.

Arrays. Exam 1 1. Java source and executable files have the following extensions? a..java and.class...

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