インタフェース(残り)

Interface variable

interface Motion{
	int NORTH = 1;
    int EAST = 2;
    int SOUTH = 3;
    int WEST = 4;
    
    void move(int direction);
    int getX();
    int getY();

}

class TwoDMotion implements Motion {
	private int posX, posY;
	public TwoDMotion() { posX = 0; posY = 0; }
    
    // 여기와 같이 interface의 변수들이 상수처럼 사용되고 있다.
	public void move(int direction) {
		if(direction == NORTH) posY--;
		else if(direction == SOUTH) posY++;
		else if(direction == EAST) posX++;
		else if(direction == WEST) posX--;
	}
    
	public int getX() { return posX; }
	public int getY() { return posY; }
}

Interface method

interface IntSequence{

	// 이러한 형태의 메소드를 factory method라고 부른다.
	static IntSequence digitsOf(int n){
		return new DigitSequence(n);
	}
    boolean hasNext();
    int next();
}

IntSequence digits = IntSequence.digitsOf(1729);

intercface IntSequence{
	default boolean hasNext() {return true;}
    int next();
}

//아래와 같이 클래스는 implements 하였지만 
//hasNext를 새롭게 정의하지 않았다.
class SquareSequence implements IntSequence{
	private int i;
    public int next(){
		i++;
        return i * i;
    }
}

interface Person {
	String getName();
	default int getId() { return 0; } 
    // Error: duplicate 		
    // default methods with the same type of parameters
}

interface Identified {
	default int getId() { return 1; } 
    // Error: duplicate 
    // default methods with the same type of parameters
}

class Employee implements Person, Identified {
	private String name;
	public Employee(String name) { this.name = name; }
	public String getName() { return this.name; }
}

public class Lecture {
	public static void main(String[] args) {
		Employee m = new Employee("Peter");
        //바로 이부분에서 문제가 생길 수 있다.
		System.out.println(m.getId());
	}
}

interface CustomInterface {
	public abstract void method1();
	public default void method2() {
		// private method를 당연하듯이 사용한다.
    		method4(); 
    		// 또한 여기와 같이 static method로 
        	// 정의된 method5가 default method에서 
        	// 호출 된 것을 확인할 수 있다.
		method5(); 
		System.out.println("default method");
	}
	public static void method3() {
		method5(); 
    	//static method inside other static method
		System.out.println("static method");
	}
	//method4 private 선언 : 함수의 구현도 해주었다.
	private void method4() {
		System.out.println("private method");
	}
	//private static method가 선언되어 있다.
	private static void method5() {
		System.out.println("private static method");
	}
}

public class Lecture implements CustomInterface {
	public void method1() {
		System.out.println("abstract method");
	}
    //현재 여기에서는 method4의 호출을 하지 않았으나 사용이 불가능하다.
	public static void main(String[] args){
		CustomInterface instance = new Lecture();
		instance.method1();
		instance.method2();
		CustomInterface.method3();
	}
}

このときいくつかのルール(試験)があります

継承

Extending a class

class Employee{
	private String name;
    private int salary;
    public Employee(){
		this.name = "NoName";
        this.salary = 0;
	}
	public String getName() {return this.name;}
    public void setName(String name) {this.name = name;}
    public int getSalary() {return this.salary;}
    public void setSalary(int salary) {this.salary = salary;}
}

class Manager extends Employee{
	private int bonus;
    public void setBonus(int bonus) {this.bonus = bonus;}
}

Super class vs Sub class

public static void main(String[] args){
	Manager m = new Manager();
    System.out.println(m.getName() + " " + m.getSalary());
}

Method overriding

class Manager extends Employee{
	private int bonus;
    public void setBonus(int bonus) {this.bonus = bonus;}
    //아래는 함수의 재정의 + superclass 함수의 사용을 보여준다.
    public int getSalary(){
		return super.getSalary()+bonus;
	}
}

class Manager extends Employee {
	private int bonus;
	public void setBonus(int bonus) { this.bonus = bonus; }
	public int getSalary() {
		return this.salary + bonus;
        // Error: salary is private in class Employee.
	}
}

class Employee {
	private String name;
	protected int salary;

	public Employee() {
		this.name = "NoName";
		this.salary = 100000;
	}
	public String getName() {return this.name;}
	public void setName(String name) {this.name = name;}
	public int getSalary() {return this.salary;}
	public void setSalary(int salary) {this.salary = salary;}
}

class Manager extends Employee{
	private int bonus = 50000;
	public void setBonus(int bonus) {this.bonus = bonus;}
	public int getSalary() {
		return super.getSalary()+bonus;
	}
}

class Employee{
	private String name;
    protected Employee supervisor;
    public Employee(){
		this.name = "NoName";
	}
    public boolean worksFor(Employee supervisor){
		System.out.println("Employee.worksFor");
        return (this.supervisor == supervisor)
	}
}

class Manager extends Employee{
	public boolean worksFor(Manager supervisor){
		System.out.println("Manager.worksFor");
        return (this.supervisor == supervisor)
	}
}

class Manager extends Employee{
	@Override
	public boolean worksFor(Manager supervisor){
		System.out.println("Manager.worksFor");
        return (this.supervisor == supervisor)
	}
}

class Employee {
	private String name;
	protected Employee supervisor;
	public Employee() {
		this.name = "NoName";
	}
	public Employee getSupervisor() {
		System.out.println("Employee");
		return supervisor;
	}
}

class Manager extends Employee {
	@Override // this is ok!
	public Manager getSupervisor() {
		System.out.println("Manager");
		return (Manager)supervisor;
	}
}

過負荷承認範囲

access modifier
承認X

もどりがた
承認X

パラメータ
承認O

@Override承認範囲

一般資料型返却型
承認X

クラスデータ戻りタイプ
承認O

クラスパラメータ
承認X