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d789391 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 | Objects formed from their own classes behave like any other objects.
That is, objects can be stored in variables and data structures, and their methods can be called in the same way
as the methods of objects created from classes that come with Java.
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Objects as method parameters and return values
Objects created from their own classes behave as method parameters and
return values in the same way as other objects.
Methods are passed a reference to a creature, so a method can (as a side effect) modify the creatures it receives as parameters.
For example, the class Student and an example of a method that prints student data:
class Student {
// ATTRIBUTES
private String name;
private String studentId;
private int studyPoints;
//CONSTRUCTOR
public Student(String name, String studentId, int studyPoints) {
this.name = name;
this.studentId = studentId;
this.studyPoints = studyPoints;
}
public String getName() {
return name;
}
public String getStudentId() {
return studentId;
}
public int getStudyPoints() {
return this.studyPoints;
}
public void setStudyPoints(int studyPoints) {
if (studyPoints >= 0) {
this.studyPoints = studyPoints;
}
}
public void addPoints(int completionPoints) {
if (completionPoints >= 0) {
this.studyPoints += completionPoints;
}
}
}
public class TestClass {
public static void main(String[] args) {
Student sally = new Student("Sally Student", "12345", 154);
printStudent(sally);
}
public static void printStudent(Student student) {
System.out.println("Name: " + student.getName());
System.out.println("St.id: " + student.getStudentId());
System.out.println("Study points: " + student.getStudyPoints());
}
}
TestClass outputs:
Name: Sally Student
St.id: 12345
Study points: 154
Next, let's define the class Course:
class Course {
private String identifier;
private int studyPoints;
public Course(String identifier, int studyPoints) {
this.identifier = identifier;
this.studyPoints = studyPoints;
}
public String getIdentifier() {
return identifier;
}
public int getStudyPoints() {
return studyPoints;
}
}
...and then a method that takes the course and the student as parameters.
The method adds the credits of the course to the credits of the student:
public class TestClass {
public static void main(String[] args) {
Student samuel = new Student("Samuel Student", "12345", 154);
Course oop = new Course("OOP", 5);
addResult(samuel, oop);
System.out.println(samuel.getStudyPoints());
}
// NEW METHOD HERE
public static void addResult(Student student, Course course) {
student.addPoints(course.getStudyPoints());
}
}
Program outputs:
159
Of course, the method can also return a new object.
The following example creates a new student object by copying the name and student number from the object given as a parameter
public class TestClass {
public static void main(String[] args) {
Student samantha = new Student("Samantha Student", "12345", 154);
Student samantha2 = copy(samantha);
System.out.println(samantha2.getName());
System.out.println(samantha2.getStudentId());
System.out.println(samantha2.getStudyPoints());
}
// FROM INPUT 'student' object
// create a 'copy/new student' object
// retrieving the input's information
public static Student copy(Student student) {
Student copy = new Student(student.getName(),
student.getStudentId(), 0);
return copy;
}
}
Program outputs:
Samantha Student
12345
0
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