Author: kpark

SliderFrame (JSlider, JLabel, JTextfield, JButton)

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.JTextField;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// SliderFrame shows ChangeListener, KeyListener, ActionListener
public class SliderFrame extends JFrame implements ChangeListener, KeyListener, ActionListener {

    JPanel panel = new JPanel(new BorderLayout());
    JPanel panel1 = new JPanel(new FlowLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);
    JTextField textfield = new JTextField(10);
    JButton button = new JButton("Close");

    public SliderFrame(String name) {
        super(name);

        this.add(panel);
        this.panel1.add(label);
        this.panel1.add(textfield);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(panel1, BorderLayout.NORTH);
        this.panel.add(button, BorderLayout.SOUTH);

        this.slider.addChangeListener(this); // ChangeListener stateChanged
        this.textfield.addKeyListener(this); // KeyListener keyTyped, keyPressed, keyReleased
        this.button.addActionListener(this); // ActionListener actionPerformed

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame("SliderFrame");
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        JSlider s = (JSlider)e.getSource();
        textfield.setText("" + s.getValue()); 
    }

    @Override
    public void keyTyped(KeyEvent e) { 
    }

    @Override
    public void keyPressed(KeyEvent e) {
    }

    @Override
    public void keyReleased(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_ENTER) {
            Toolkit.getDefaultToolkit().beep(); 
            System.out.println("ENTER pressed");
            JTextField t = (JTextField) e.getSource();
            int value = Integer.parseUnsignedInt(t.getText());
            slider.setValue(value);
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        JButton b = (JButton)e.getSource();
        if (b == button) {
            this.setVisible(false);
            this.dispose();
        }
    }
}

Slider(JSlider, JLabel)
1. event listener using anonymous class

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// SliderFrame1 shows event listener using anonymous class
public class SliderFrame1 extends JFrame {

    JPanel panel = new JPanel(new BorderLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);

    public SliderFrame1(String name) {
        super(name);

        this.add(panel);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(label, BorderLayout.SOUTH);

        // using anonymous class
        this.slider.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSlider s = (JSlider)e.getSource();
                label.setText("Value : " + s.getValue());
            }
        });

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame1("SliderTest1");
    }
}

2. event listener using interface implements

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// using implements ChangeListener
public class SliderFrame2 extends JFrame implements ChangeListener {

    JPanel panel = new JPanel(new BorderLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);

    public SliderFrame2(String name) {
        super(name);

        this.add(panel);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(label, BorderLayout.SOUTH);

        this.slider.addChangeListener(this); // implements ChangeListener

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame2("SliderTest2");
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        JSlider s = (JSlider)e.getSource();
        label.setText("Value : " + s.getValue());
    }
}

3. event listener using private inner class

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class SliderFrame3 extends JFrame {

    JPanel panel = new JPanel(new BorderLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);

    // using private inner class
    private class SliderChangeListener implements ChangeListener {
        @Override
        public void stateChanged(ChangeEvent e) {
            JSlider s = (JSlider)e.getSource();
            label.setText("Value : " + s.getValue());
        }
    }

    public SliderFrame3(String name) {
        super(name);
        this.add(panel);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(label, BorderLayout.SOUTH);

        this.slider.addChangeListener(new SliderChangeListener()); // private class

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame3("SliderTest3");
    }
}

4. event listener using outer class

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// using private inner class
class SliderChangeListener implements ChangeListener {
    JLabel label = null;
    public SliderChangeListener(JLabel label) {
        this.label = label;
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        JSlider s = (JSlider)e.getSource();
        label.setText("Value : " + s.getValue());
    }
}

public class SliderFrame4 extends JFrame {

    JPanel panel = new JPanel(new BorderLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);

    public SliderFrame4(String name) {
        super(name);
        this.add(panel);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(label, BorderLayout.SOUTH);

        this.slider.addChangeListener(new SliderChangeListener(this.label)); // outer class

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame4("SliderTest4");
    }
}

5. event listener using lambda

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// SliderFrame5 shows event listener using lambda
public class SliderFrame5 extends JFrame {

    JPanel panel = new JPanel(new BorderLayout());
    JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 100, 20);
    JLabel label = new JLabel("Value : ", JLabel.CENTER);

    public SliderFrame5(String name) {
        super(name);

        this.add(panel);
        this.panel.add(slider, BorderLayout.CENTER);
        this.panel.add(label, BorderLayout.SOUTH);

        // using lambda
        this.slider.addChangeListener(e -> { // lambda
                JSlider s = (JSlider)e.getSource();
                label.setText("Value : " + s.getValue());
        });

        this.setSize(250, 150);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new SliderFrame5("SliderTest5");
    }
}

https://www.javatpoint.com/java-layout-manager
java.awt.BorderLayout
java.awt.FlowLayout
java.awt.GridLayout
java.awt.CardLayout
java.awt.GridBagLayout
javax.swing.BoxLayout
javax.swing.GroupLayout
javax.swing.ScrollPaneLayout
javax.swing.SpringLayout etc.

https://www.javatpoint.com/java-swing
https://www.javatpoint.com/java-jbutton
https://www.javatpoint.com/java-jlabel
https://www.javatpoint.com/java-jtextfield
https://www.javatpoint.com/java-jcheckbox
https://www.javatpoint.com/java-jradiobutton
https://www.javatpoint.com/java-jcombobox
https://www.javatpoint.com/java-jtable
https://www.javatpoint.com/java-jslider
https://www.javatpoint.com/java-jdialog
https://www.javatpoint.com/java-jpanel
https://www.javatpoint.com/java-jfilechooser
https://www.javatpoint.com/java-jtogglebutton
https://www.javatpoint.com/java-jframe
https://www.javatpoint.com/java-jscrollpane

ShapePolymorphism-Interface

Shape 추상클래스 has-a ShapeType, ShapeColor, ShapeRect

Shape 추상클래스를 상속받은 Triangle, Rectangle, Square, Circle 클래스는 추상메소드인 void area()를 반드시 구현하였다.

Shape 추상클래스는 Moveable, Scalable 인터페이스를 상속하여 추상메소드인 Moveable 인터페이스의 void move(int, int)와 Scalable 인터페이스의 void scale(int)를 구현하였다.

import java.util.*;

class Person implements Comparable<Person> {
    private static int count = 0; // static (class) field
    protected String name; // instance field
    protected int age; // instance field

    public Person() {
        //System.out.println("Person Constructor"); // this("", 0); error: call to this must be first statemenht in constructor
        this("", 0);
    }

    public Person(String name, int age) {
        count++;
        this.name = name;
        this.age = age;
    }

    public Person(Person other) {
        this(other.name, other.age);
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void set(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void set(Person other) {
        this.name = other.name;
        this.age = other.age;
    }

    public Person clone() {
        Person p = new Person(this.name, this.age);
        return p;
    }

    @Override
    public boolean equals(Object other) { // Object.equals overriding
        if (other instanceof Person) {
            Person that = (Person) other;
            return that.canEqual(this) && this.getName().equals(that.getName()) && this.getAge() == that.getAge();
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (41 * getName().hashCode() + getAge());
    }

    public boolean canEqual(Object other) {
        return (other instanceof Person);
    }

    @Override
    public String toString() { // Object.toString() overriding
        return "Person Name: " + name + " Age: " + age;
    }

    public void print() { // instance methods
        System.out.println("Person Name: " + name + " Age: " + age);
    }

    public static void printCount() { // static (class) methods
        System.out.println("Person Count: " + count);
    }

    public static int getCount() {  // static (class) methods
        return count; 
    }

    public static void setCount(int value) { // static (class) methods
        count = value; 
    } 

    public int compareTo(Person other) {
        String thisName = this.getName().toUpperCase();
        String otherName = ((Person)other).getName().toUpperCase();
        //ascending order
        return thisName.compareTo(otherName);
        //descending order
        //return otherName.compareTo(thisName);
    }

    public static Comparator<Person> AgeComparator = new Comparator<Person>() {
        public int compare(Person p1, Person p2) {
            int age1 = p1.getAge();
            int age2 = p2.getAge();
            //ascending order
            return age1 – age2;
            //descending order
            //return age2 – age1;
        }
    };
}

///////////////////////////////////////////////////////////////////////////////////////
class Student extends Person {
    private static int count = 0; // static (class) field
    protected int id;

    public Student() {
        id = 5208;
    }

    public Student(String name, int age, int id) {
        super(name, age);
        this.id = id;
        count++;
    }

    public int getID() {
        return id;
    }

    public void setID(int id) {
        this.id = id;
    }

    public void set(String name, int age, int id) {
        super.set(name, age);
        this.id = id;
    }

    public void set(String name, int age) {
        super.set(name, age);
    }

    public void set(Student other) {
        this.set(other.name, other.age, other.id);
    }

    public void set(Person other) {
        if (other instanceof Person)
            super.set(other);
        else
            this.set((Student)other);
    }

    public Student clone() {
        Student s = new Student(this.name, this.age, this.id);
        return s;
    }

    @Override
    public boolean equals(Object other) { // Object.equals overriding
        if (other instanceof Student) {
            Student that = (Student) other;
            return that.canEqual(this) && this.getName().equals(that.getName()) && this.getAge() == that.getAge() && this.getID() == that.getID();
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (41 * super.hashCode() + getID());
    }

    public boolean canEqual(Object other) {
        return (other instanceof Student);
    }

    @Override
    public String toString() { // Object.toString() overriding
        return "Student Name: " + name + " Age: " + age + " ID: " + id;
    }

    public void superPrint() {
        super.print();
    }

    public void print() { // Person.print() method overriding
        System.out.println("Student Name: " + name + " Age: " + age + " ID: " + id);
    }

    public static void printCount() { // static (class) methods
        System.out.println("Student Count: " + count);
    }

    public static int getCount() { // static (class) methods
        return count; 
    } 
    public static void setCount(int value) { // static (class) methods
        count = value; 
    }

    public int compareTo(Student other) {
        String thisName = this.getName().toUpperCase();
        String otherName = ((Student)other).getName().toUpperCase();
        //ascending order
        return thisName.compareTo(otherName);
        //descending order
        //return otherName.compareTo(thisName);
    }

    public static Comparator<Student> AgeComparator = new Comparator<Student>() {
        public int compare(Student p1, Student p2) {
            int age1 = p1.getAge();
            int age2 = p2.getAge();
            //ascending order
            return age1 – age2;
            //descending order
            //return age2 – age1;
        }
    };

    public static Comparator<Student> IDComparator = new Comparator<Student>() {
        public int compare(Student p1, Student p2) {
            int id1 = p1.getID();
            int id2 = p2.getID();
            //ascending order
            return id1 – id2;
            //descending order
            //return id2 – id1;
        }
    };
}

class PersonStudentTest {

    public static void print(Object[] array) {
        for(Object o : array) {
            System.out.println(o);
        }
    }

    public static void main(String[] args) {
///////////////////////////////////////////////////////////////////////
        Person jason1 = new Person("Jason", 10);
        Person jason2 = new Person("Jason", 10);
        Person jason3 = jason1;
        Person jason4 = new Person("Jason", 20);

        if (jason1 == jason2)
            System.out.println("jason1 == jason2");
        else
            System.out.println("jason1 != jason2"); // 동일한 reference를 가리키지 않으므로 jason1 != jason2

        if (jason1 == jason3)
            System.out.println("jason1 == jason3"); // 동일한 reference이므로 jason1 == jason3
        else
            System.out.println("jason1 != jason3");

        if (jason1.equals(jason4))
            System.out.println("jason1 == jason4");
        else
            System.out.println("jason1 != jason4"); // 동일한 reference를 가리키지 않으므로 jason1 != jason4

        if (jason1.equals(jason2))
            System.out.println("jason1 equals to jason2"); // 내용이 같으므로 jason1 equals to jason2
        else
            System.out.println("jason1 is not equal to jason2");

        if (jason1.equals(jason3))
            System.out.println("jason1 equals to jason3"); // 내용이 같으므로 jason1 equals to jason3
        else
            System.out.println("jason1 is not equal to jason3");

        if (jason1.equals(jason4))
            System.out.println("jason1 equals jason4");
        else
            System.out.println("jason1 is not equal to jason4"); // 내용이 다르므로 jason1 is not equal to jason4

///////////////////////////////////////////////////////////////////////
        Student john1 = new Student("John", 10, 100);
        Student john2 = new Student("John", 10, 100);
        Student john3 = john1;
        Student john4 = new Student("John", 20, 100);

        if (john1.equals(john2))
            System.out.println("john1 equals to john2"); // 내용이 같으므로 john1 equals to john2
        else
            System.out.println("john1 is not equal to john2");

        if (john1.equals(john3))
            System.out.println("john1 equals to john3"); // 내용이 같으므로 john1 equals to john3
        else
            System.out.println("john1 is not equal to john3");

        if (john1.equals(john4))
            System.out.println("john1 equals to john4");
        else
            System.out.println("john1 is not equal to john4"); // 내용이 다르므로 john1 is not equal to john4

///////////////////////////////////////////////////////////////////////
        Student[] sList = new Student[3];
        sList[0] = new Student("Kevin", 0, 222);
        sList[1] = new Student("Jason", 1, 333);
        sList[2] = new Student("John", 2, 111);

        System.out.println("STUDENT SORT BY NAME (DEFAULT)!!!");
        Arrays.sort(sList);
        print(sList);

        System.out.println("STUDENT SORT by AGE!!!");
        Arrays.sort(sList, Student.AgeComparator);
        print(sList);

        System.out.println("STUDENT SORT by ID!!!");
        Arrays.sort(sList, Student.IDComparator);
        print(sList);

///////////////////////////////////////////////////////////////////////
        Student[] sList2 = new Student[3];
        sList2[0] = new Student("Kevin", 0, 222);
        sList2[1] = new Student("Jason", 1, 333);
        sList2[2] = new Student("John", 2, 111);

        System.out.println("STUDENT SORT BY NAME (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getName().toUpperCase().compareTo(s2.getName().toUpperCase());
            }
        });
        print(sList2);

        System.out.println("STUDENT SORT by AGE (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getAge() – s2.getAge();
            }
        });
        print(sList2);

        System.out.println("STUDENT SORT by ID (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getID() – s2.getID();
            }
        });
        print(sList2);

///////////////////////////////////////////////////////////////////////
        Student[] sList3 = sList2;

        System.out.println("STUDENT SORT BY NAME (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            ss1.getName().compareTo(ss2.getName())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

        System.out.println("STUDENT SORT by AGE (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            Integer.compare(ss1.getAge(), ss2.getAge())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

        System.out.println("STUDENT SORT by ID (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            Integer.compare(ss1.getID(), ss2.getID())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

///////////////////////////////////////////////////////////////////////
        List<Student> sList4 = new ArrayList<Student>();
        sList4.add(new Student("Kevin", 0, 222));
        sList4.add(new Student("Jason", 1, 333));
        sList4.add(new Student("John", 2, 111));

        System.out.println("STUDENTLIST SORT BY NAME (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getName().compareTo(ss2.getName())
        );
        sList4.forEach((s) -> System.out.println(s));

        System.out.println("STUDENTLIST SORT by AGE (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getAge() – ss2.getAge()
        );
        sList4.forEach((s) -> System.out.println(s));

        System.out.println("STUDENTLIST SORT by ID (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getID() – ss2.getID()
        );
        sList4.forEach((s) -> System.out.println(s));
    }

}

import java.util.*;

class Person implements Comparable<Person> {
    private static int count = 0; // static (class) field
    protected String name; // instance field
    protected int age; // instance field

    public Person() {
        //System.out.println("Person Constructor"); // this("", 0); error: call to this must be first statemenht in constructor
        this("", 0);
    }

    public Person(String name, int age) {
        count++;
        this.name = name;
        this.age = age;
    }

    public Person(Person other) {
        this(other.name, other.age);
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void set(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void set(Person other) {
        this.name = other.name;
        this.age = other.age;
    }

    public Person clone() {
        Person p = new Person(this.name, this.age);
        return p;
    }

    @Override
    public boolean equals(Object other) { // Object.equals overriding
        if (other instanceof Person) {
            Person that = (Person) other;
            return that.canEqual(this) && this.getName().equals(that.getName()) && this.getAge() == that.getAge();
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (41 * getName().hashCode() + getAge());
    }

    public boolean canEqual(Object other) {
        return (other instanceof Person);
    }

    @Override
    public String toString() { // Object.toString() overriding
        return "Person Name: " + name + " Age: " + age;
    }

    public void print() { // instance methods
        System.out.println("Person Name: " + name + " Age: " + age);
    }

    public static void printCount() { // static (class) methods
        System.out.println("Person Count: " + count);
    }

    public static int getCount() {  // static (class) methods
        return count; 
    }

    public static void setCount(int value) { // static (class) methods
        count = value; 
    } 

    public int compareTo(Person other) {
        String thisName = this.getName().toUpperCase();
        String otherName = ((Person)other).getName().toUpperCase();
        //ascending order
        return thisName.compareTo(otherName);
        //descending order
        //return otherName.compareTo(thisName);
    }

    public static Comparator<Person> AgeComparator = new Comparator<Person>() {
        public int compare(Person p1, Person p2) {
            int age1 = p1.getAge();
            int age2 = p2.getAge();
            //ascending order
            return age1 – age2;
            //descending order
            //return age2 – age1;
        }
    };
}

///////////////////////////////////////////////////////////////////////////////////////
class Student extends Person {
    private static int count = 0; // static (class) field
    protected int id;

    public Student() {
        id = 5208;
    }

    public Student(String name, int age, int id) {
        super(name, age);
        this.id = id;
        count++;
    }

    public int getID() {
        return id;
    }

    public void setID(int id) {
        this.id = id;
    }

    public void set(String name, int age, int id) {
        super.set(name, age);
        this.id = id;
    }

    public void set(String name, int age) {
        super.set(name, age);
    }

    public void set(Student other) {
        this.set(other.name, other.age, other.id);
    }

    public void set(Person other) {
        if (other instanceof Person)
            super.set(other);
        else
            this.set((Student)other);
    }

    public Student clone() {
        Student s = new Student(this.name, this.age, this.id);
        return s;
    }

    @Override
    public boolean equals(Object other) { // Object.equals overriding
        if (other instanceof Student) {
            Student that = (Student) other;
            return that.canEqual(this) && this.getName().equals(that.getName()) && this.getAge() == that.getAge() && this.getID() == that.getID();
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (41 * super.hashCode() + getID());
    }

    public boolean canEqual(Object other) {
        return (other instanceof Student);
    }

    @Override
    public String toString() { // Object.toString() overriding
        return "Student Name: " + name + " Age: " + age + " ID: " + id;
    }

    public void superPrint() {
        super.print();
    }

    public void print() { // Person.print() method overriding
        System.out.println("Student Name: " + name + " Age: " + age + " ID: " + id);
    }

    public static void printCount() { // static (class) methods
        System.out.println("Student Count: " + count);
    }

    public static int getCount() { // static (class) methods
        return count; 
    } 
    public static void setCount(int value) { // static (class) methods
        count = value; 
    }

    public int compareTo(Student other) {
        String thisName = this.getName().toUpperCase();
        String otherName = ((Student)other).getName().toUpperCase();
        //ascending order
        return thisName.compareTo(otherName);
        //descending order
        //return otherName.compareTo(thisName);
    }

    public static Comparator<Student> AgeComparator = new Comparator<Student>() {
        public int compare(Student p1, Student p2) {
            int age1 = p1.getAge();
            int age2 = p2.getAge();
            //ascending order
            return age1 – age2;
            //descending order
            //return age2 – age1;
        }
    };

    public static Comparator<Student> IDComparator = new Comparator<Student>() {
        public int compare(Student p1, Student p2) {
            int id1 = p1.getID();
            int id2 = p2.getID();
            //ascending order
            return id1 – id2;
            //descending order
            //return id2 – id1;
        }
    };
}

class PersonStudentTest {

    public static void print(Object[] array) {
        for(Object o : array) {
            System.out.println(o);
        }
    }

    public static void main(String[] args) {
///////////////////////////////////////////////////////////////////////
        Student[] sList = new Student[3];
        sList[0] = new Student("Kevin", 0, 222);
        sList[1] = new Student("Jason", 1, 333);
        sList[2] = new Student("John", 2, 111);

        System.out.println("STUDENT SORT BY NAME (DEFAULT)!!!");
        Arrays.sort(sList);
        print(sList);

        System.out.println("STUDENT SORT by AGE!!!");
        Arrays.sort(sList, Student.AgeComparator);
        print(sList);

        System.out.println("STUDENT SORT by ID!!!");
        Arrays.sort(sList, Student.IDComparator);
        print(sList);

///////////////////////////////////////////////////////////////////////
        Student[] sList2 = new Student[3];
        sList2[0] = new Student("Kevin", 0, 222);
        sList2[1] = new Student("Jason", 1, 333);
        sList2[2] = new Student("John", 2, 111);

        System.out.println("STUDENT SORT BY NAME (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getName().toUpperCase().compareTo(s2.getName().toUpperCase());
            }
        });
        print(sList2);

        System.out.println("STUDENT SORT by AGE (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getAge() – s2.getAge();
            }
        });
        print(sList2);

        System.out.println("STUDENT SORT by ID (anonymous method)!!!");
        Arrays.sort(sList2, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getID() – s2.getID();
            }
        });
        print(sList2);

///////////////////////////////////////////////////////////////////////
        Student[] sList3 = sList2;

        System.out.println("STUDENT SORT BY NAME (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            ss1.getName().compareTo(ss2.getName())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

        System.out.println("STUDENT SORT by AGE (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            Integer.compare(ss1.getAge(), ss2.getAge())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

        System.out.println("STUDENT SORT by ID (lambda)!!!");
        Arrays.sort(sList3, (Student ss1, Student ss2) ->
                            Integer.compare(ss1.getID(), ss2.getID())
        );
        Arrays.stream(sList3).forEach((s) -> System.out.println(s));

///////////////////////////////////////////////////////////////////////
        List<Student> sList4 = new ArrayList<Student>();
        sList4.add(new Student("Kevin", 0, 222));
        sList4.add(new Student("Jason", 1, 333));
        sList4.add(new Student("John", 2, 111));

        System.out.println("STUDENTLIST SORT BY NAME (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getName().compareTo(ss2.getName())
        );
        sList4.forEach((s) -> System.out.println(s));

        System.out.println("STUDENTLIST SORT by AGE (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getAge() – ss2.getAge()
        );
        sList4.forEach((s) -> System.out.println(s));

        System.out.println("STUDENTLIST SORT by ID (lambda)!!!");
        sList4.sort((Student ss1, Student ss2) ->
                    ss1.getID() – ss2.getID()
        );
        sList4.forEach((s) -> System.out.println(s));
    }

}

Abstract Class (추상 클래스)는 반드시 하나 이상의 abstract method(추상메소드)를 가지며, 객체를 생성할 수 없다.

Abstract Method (추상 메소드)는 구현 내용이 없는 메소드이다.

추상클래스를 상속받은 하위클래스는 반드시 추상 메소드를 재정의(method override) 구현해야한다.

Polymorphism (다형성)은 프로그램 실행(run-time execution)시 형(type)이 변화되는 객체.

다형성에 따라서, 클래스 상속관계(Inheritance)에서 메소드 재정의(Method overriding)된 것이 동적 바인딩(dynamic binding)으로 호출되었을 시,  해당 객체에 맞는 재정의된 메소드가 호출되는 것이다.

 

ShapePolymorphism

Shape 추상클래스 has-a ShapeType, ShapeColor, ShapeRect

Shape 추상클래스를 상속받은 Triangle,  Rectangle, Square, Circle 클래스는 추상메소드인 area()를 반드시 구현해야한다.

https://www.cs.usfca.edu/~wolber/SoftwareDev/OO/abstractInterfacesIntro.htm