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Transcript of 1 Training Lecture 1. 2 Primitive Data Declaration and Assignments Code State of Memory int...
1
Training Lecture 1
2
Primitive Data Declaration and Assignments
Code State of Memory
int firstNumber, secondNumber;firstNumber = 234;secondNumber = 87;
AA
int firstNumber, secondNumber;int firstNumber, secondNumber;
BBfirstNumber = 234;firstNumber = 234;secondNumber = 87;secondNumber = 87;
int firstNumber, secondNumber;int firstNumber, secondNumber;firstNumber = 234;firstNumber = 234;secondNumber = 87;secondNumber = 87;
firstNumber
secondNumber
A. A. Variables are allocated in memory.
A. A. Variables are allocated in memory.
B. B. Values are assigned to variables.
B. B. Values are assigned to variables.
234
87
3
Assigning Numerical Data
Code State of Memory
int number;int number;number = 237;number = 237;number = 35;number = 35; number
A. A. The variable is allocated in memory.
A. A. The variable is allocated in memory.
B. B. The value 237237 is assigned to numbernumber.
B. B. The value 237237 is assigned to numbernumber.
237
int number;int number;
number = 237;number = 237;
number = 35;number = 35;
AAint number;int number;
BBnumber = 237;number = 237;
CCnumber = 35;number = 35;
C. C. The value 3535 overwrites the
previous value 237.237.
C. C. The value 3535 overwrites the
previous value 237.237.
35
Assigning Objects
Code State of Memory
Customer var;Customer var;var = new Customer( );var = new Customer( );var = new Customer( );var = new Customer( );
var
A. A. The variable is allocated in memory.
A. A. The variable is allocated in memory.Customer var;Customer var;
var = new Customer( );var = new Customer( );
var = new Customer( );var = new Customer( );
AA
Customer var;Customer var;BB
var = new Customer( );var = new Customer( );
CC
var = new Customer( );var = new Customer( );B. B. The reference to the
new object is assigned to varvar.
B. B. The reference to the new object is assigned to varvar.
CustomerCustomer
C. C. The reference to another object overwrites the reference in var.var.
C. C. The reference to another object overwrites the reference in var.var.
CustomerCustomer
Having Two References to a Single Object
Code State of Memory
Customer clemens, twain;Customer clemens, twain;clemens = new Customer( );clemens = new Customer( );twain = clemens;twain = clemens;
Customer clemens, twain,Customer clemens, twain,
clemens = new Customer( );clemens = new Customer( );
twain = clemens;twain = clemens;
AA
Customer clemens, twain;Customer clemens, twain; BB
clemens = new Customer( );clemens = new Customer( );
CC
twain = clemens;twain = clemens;
A. A. Variables are allocated in memory.
A. A. Variables are allocated in memory.
clemens
twain
B. B. The reference to the new object is assigned to clemensclemens.
B. B. The reference to the new object is assigned to clemensclemens.
CustomerCustomer
C. C. The reference in clemensclemens is assigned to
customer.customer.
C. C. The reference in clemensclemens is assigned to
customer.customer.
Object Creation
myWindow = new JFrame ( ) ;
MoreExamples
Customer Customer customer;customer = new Customer( );jon = new Student(“John Java”);car1 = new Vehicle( );
Object NameName of the object we are creating here.
Object NameName of the object we are creating here.
Class NameAn instance of this class is created.
Class NameAn instance of this class is created.
ArgumentNo arguments are used here.
ArgumentNo arguments are used here.
Declaration vs. Creation
Customer customer;
customer = new Customer( );
Customer customer;
customer = new Customer( );
1. The identifier customer is declared and space is allocated in memory.
1. The identifier customer is declared and space is allocated in memory.
2. A Customer object is created and the identifier customer is set to refer to it.
2. A Customer object is created and the identifier customer is set to refer to it.
1
2
customer
1
: Customer2
State-of-Memory vs. Program
customer
: Customer
State-of-MemoryNotation
customer : Customer
Program DiagramNotation
Class NameClass NameObject NameObject Name
Name vs. Objects
Customer customer;
customer = new Customer( );
customer = new Customer( );
Customer customer;
customer
customer = new Customer( );
customer = new Customer( );
: Customer : CustomerCreated with the first new.
Created with the first new.
Created with the second new. Reference to the first Customer object is lost.
Created with the second new. Reference to the first Customer object is lost.
JFrame myWindow;
myWindow = new JFrame( );
myWindow.setSize(300, 200);
myWindow.setTitle (“My First Java Program”);
myWindow.setVisible(true);
Execution Flow
myWindow.setSize(300, 200);
Jframe myWindow;
myWindow
myWindow.setVisible(true);
State-of-Memory Diagram
: JFrame
width
height
title
visible
200
My First Java …
300
true
myWindow = new JFrame( );
myWindow.setTitle (“My First Java Program”);
The diagram shows only four of the many data members of a JFrame object.
The diagram shows only four of the many data members of a JFrame object.
Program Code
4th Ed Chapter 5 - 18
Using == With Objects (Sample 1)String str1 = new String("Java");String str2 = new String("Java");
if (str1 == str2) {System.out.println("They are equal");
} else {System.out.println("They are not equal");
}
They are not equal
Not equal because str1 and str2 point to different String objects.
4th Ed Chapter 5 - 19
Using == With Objects (Sample 2)String str1 = new String("Java");String str2 = str1;
if (str1 == str2) {System.out.println("They are equal");
} else {System.out.println("They are not equal");
}
They are equal It's equal here because str1 and str2 point to the same object.
4th Ed Chapter 5 - 20
Using equals with String
String str1 = new String("Java");String str2 = new String("Java");
if (str1.equals(str2)) {System.out.println("They are equal");
} else {System.out.println("They are not equal");
}
They are equal It's equal here because str1 and str2 have the same sequence of characters.
4th Ed Chapter 5 - 21
The Semantics of ==
4th Ed Chapter 5 - 22
In Creating String Objects
Example 1
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25
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Example 2
enter the number of Sayarat that you want to process 3enter the owner then price then model you want to processali87000teriosali 's Car ,price : 87000.0model : terios
The tax will be 1000 SR enter the owner then price then model you want to process mohamed90000camrymohamed 's Car ,price : 90000.0 model : camry
The tax will be 1000 SR enter the owner then price then model you want to process
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END of
Training Lecture 1