Java Basics 108 – Class and Object
STEPS
1) Create New Project.
Project Name: exams
Main Class: exams.ExamDetails
New Project created.
Make a copy of Startup Codes
package exams;
public class ExamDetails {
public static void main(String[] args) {
// TODO code application logic here
}
}
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2) CREATE JAVA CLASS
2-1) Delete all original codes and paste the Startup Codes above.
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public class ExamDetails
{
public static void main (String[] args){
// TODO code application logic here
}
}
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2-2) Add second class StudentResults
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public class ExamDetails {
public static void main(String[] args) {
// TODO code application logic here
}
}
class StudentResults {
}
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2-3) Add properties to the StudentResults class.
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public class ExamDetails {
public static void main(String[] args) {
// TODO code application logic here
}
}
class StudentResults {
String Full_Name;
String Exam_Name;
String Exam_Score;
String Exam_Grade;
}
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2-4) Declare a StudentResults object called aStudent
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
}
}
class StudentResults {
String Full_Name;
String Exam_Name;
String Exam_Score;
String Exam_Grade;
}
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2-5) Assign property value to aStudent
Try printing the value.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
aStudent.Exam_Name = "VB.NET";
String exam = aStudent.Exam_Name;
System.out.println(exam);
}
}
class StudentResults {
String Full_Name;
String Exam_Name;
String Exam_Score;
String Exam_Grade;
}
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2-6) Change access to class property in StudentResults.
Try running the code.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent= new StudentResults();
aStudent.Exam_Name="VB.NET";
String exam=aStudent.Exam_Name;
System.out.println(exam);
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
}
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At this point, the compiler will output error message:
Comment (//) those lines that have got errors.
2-7) Add an initiating method (Constructor ) to StudentResults.
a) The name of the method is similar to the name of the class.
b) The parameters of the method are assigned to the property of the class.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
//aStudent.Exam_Name = "VB.NET";
//String exam = aStudent.Exam_Name;
//System.out.println(exam);
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults(String name, String grade) {
Full_Name = name;
Exam_Grade = grade;
}
}
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At this point, if you try to compile, you may get errors because the new object declaration parameter doesn’t match with the constructor parameter declaration.
2-8) Change the constructor declaration.
a) Omitting parameter
b) Assigning default values to all class properties.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults() {
Full_Name="No name given";
Exam_Name="Unknown";
Exam_Score="No Score";
Exam_Grade="Unknown";
}
}
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Note: delete the statement marked with “//”
2-9) Create method to change class property.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults() {
Full_Name = "No name given";
Exam_Name = "Unknown";
Exam_Score = "No Score";
Exam_Grade = "Unknown";
}
String fullName(String aName) {
Full_Name = aName;
return Full_Name;
}
}
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2-10) Edit the main method.
a) Add a call to class method.
b) Add an output statement to print the class property value.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
String sName = aStudent.fullName("Bill Gates");
System.out.println(sName);
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults() {
Full_Name = "No name given";
Exam_Name = "Unknown";
Exam_Score = "No Score";
Exam_Grade = "Unknown";
}
String fullName(String aName) {
Full_Name = aName;
}
}
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2-11) Add another method to class StudentResults
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
String sName = aStudent.fullName("Bill Gates");
System.out.println(sName);
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults() {
Full_Name = "No name given";
Exam_Name = "Unknown";
Exam_Score = "No Score";
Exam_Grade = "Unknown";
}
String fullName(String aName) {
Full_Name = aName;
return Full_Name;
}
String examName(String examCode){
if (examCode.equals("VB")){
Exam_Name="Visual Basic.NET";
}
else if (examCode.equals("JV")){
Exam_Name="Java";
}
else if (examCode.equals("C#")){
Exam_Name="C# .NET";
}
else if (examCode.equals("PH")){
Exam_Name="PHP";
}
else {
Exam_Name="No Exam Selected";
}
return Exam_Name;
}
}
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2-12) Edit main method
a) Add a call to the new class method.
b) Add an output statement to print the returning value.
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public class ExamDetails {
public static void main(String[] args) {
StudentResults aStudent = new StudentResults();
String sName = aStudent.fullName("Bill Gates");
String exam = aStudent.examName("VB");
System.out.println(sName);
System.out.println(exam);
}
}
class StudentResults {
private String Full_Name;
private String Exam_Name;
private String Exam_Score;
private String Exam_Grade;
StudentResults() {
Full_Name = "No name given";
Exam_Name = "Unknown";
Exam_Score = "No Score";
Exam_Grade = "Unknown";
}
String fullName(String aName) {
Full_Name = aName;
return Full_Name;
}
String examName(String examCode) {
if (examCode.equals("VB")) {
Exam_Name = "Visual Basic.NET";
} else if (examCode.equals("JV")) {
Exam_Name = "Java";
} else if (examCode.equals("C#")) {
Exam_Name = "C# .NET";
} else if (examCode.equals("PH")) {
Exam_Name = "PHP";
} else {
Exam_Name = "No Exam Selected";
}
return Exam_Name;
}
}
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3) More Class Methods
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