Month: May 2018

CarSedan-PublicProtectedPrivate

public class Car {
    // member field
    private boolean disel; // private은 파생 클래스에서 사용하지 못함
    protected boolean gasoline; // protected은 파생 클래스에서 사용 가능하나 외부(다른 패키지)에서는 호출하지 못함
    protected int wheel = 4;

    // constructor
    protected Car() { 
        disel = true; 
        gasoline = true; 
    }
    protected Car(int wheel) { 
        this.wheel = wheel; 
        disel = false; 
        gasoline = false; 
    }

    // method
    protected void move() {
        if (disel) System.out.println("Disel Car");
        System.out.println("Move wheel=" + wheel);
    }
}

public class Sedan extends Car {
    // member field
    private boolean gasoline; // 파생 클래스에서 기반클래스에 멤버필드명이 같다면 default는 자신의 멤버부터 호출, 즉, this.gasoline 부터 사용

    // constructor
    public Sedan() { // 내부적으로 super() 호출, 즉 super.gasoline=true 
        gasoline = false; 
    } 
    public Sedan(int wheel) { // super(int wheel)를 호출, 즉 super.gasoline=false (protected 생성자는 파생클래스에서 호출 가능)
        super(wheel); 
        gasoline = true; 
    } 
    // method
    public void sedanMove() {
        // base의 gasoline과 this의 gasoline을 구분해야하는 경우
        if (super.gasoline) System.out.print("Gasoline Car ");
        if (this.gasoline) System.out.print("Gasoline SedanCar ");
        System.out.println("move wheel=" + wheel);
    }

    public static void main(String[] args) {
        Car myCar = new Car(); // protected 생성자 같은 패키지 내에 사용가능.
        myCar.move(); // protected 메소드 호출 가능
        System.out.println("myCar wheel=" + myCar.wheel); // protected 필드 호출 가능

        // 바퀴 4개 디젤 자동차
        Sedan myCar1 = new Sedan(); // public 생성자 호출 가능
        myCar1.move(); // protected 메소드 호출 가능
        myCar1.sedanMove(); // public 메소드 호출가능

        // 바퀴 6개 가솔린 자동차
        Sedan myCar2 = new Sedan(6); // public 생성자 호출 가능
        myCar2.move(); // protected 메소드 호출 가능
        myCar2.sedanMove(); // public 메소드 호출가능
    }
}

BankAccount-InstanceStatic – instance vs static member field & method
BankAccount

public class BankAccount {
    protected String name; // instance field
    protected double balance; // instance field 
    protected static double interestRate; // static field

    public BankAccount() { // default constructor
        this(1000, "JAVA17");
    }

    public BankAccount(String name, double balance) {
        this.name = name;
        this.balance = balance;
        BankAccount.interestRate = 1.0;
    }

    public void deposit(double amount) { // instance method
        balance += amount;
    }

    public void withdraw(double amount) { // instance method
        balance -= amount;
    }

    public void transfer(double amount, BankAccount other) { // instance method
        withdraw(amount);
        other.deposit(amount);
    }

    public double getBalance() { // instance method
        return balance + balance * interestRate * 0.01;
    }

    public void print() { // instance method
        System.out.println(name + " balance=" + getBalance());
    }

    @Override // Object.toString() method override
    public String toString() { // instance method
        return name + " balance=" + getBalance();
    }

    public static void setInterestRate(double interestRate) { // static method
        BankAccount.interestRate = interestRate;
    }
}

public class CheckingAccount extends BankAccount {
    private double overdraftLimit; 

    public CheckingAccount(String name, double balance, double overdraftLimit) { 
        super(name, balance);
        interestRate = 2.0;
        setOverdraftLimit(overdraftLimit); 
    }
	
    public void setOverdraftLimit(double overdraftLimit) {  
        this.overdraftLimit = overdraftLimit;  
    }  

    public double getOverdraftLimit() {  
        return overdraftLimit;  
    }

    @Override // BankAccount.withdraw(double amount) method override 
    public void withdraw(double amount) {  
        if(getBalance() - overdraftLimit < amount)
            System.out.println("CheckingAccount::withdraw Cannot be withdrawn due to overdraftLimit"); 
        else
            super.withdraw(amount);  		
    }

    @Override // BankAccount.print() method override 
    public void print() {
        System.out.println("CheckingAccount: " + name + " balance=" + getBalance());
    }
}

public class SavingAccount extends BankAccount {
    public SavingAccount(String name, double balance) { 
        super(name, balance);
        interestRate = 5.0;
    }

    @Override // BankAccount.withdraw(double amount) method override
    public void withdraw(double amount)  {
        if (getBalance() < amount)  
            System.out.println("SavingAccount::withdraw Amount is larger than current balance.");  
        else
            super.withdraw(amount);
    }

    @Override // BankAccount.print() method override 
    public void print() {
        System.out.println("SavingAccount: " + name + " balance=" + getBalance());
    }
}

public class BankAccountTest {
    public static void main(String[] args) {
        BankAccount b1 = new BankAccount("P", 0);
        b1.deposit(3000);
        b1.withdraw(1000);
        b1.print(); // P balance=2020.0

        BankAccount b2 = new BankAccount("K", 0);
        b1.print(); // K balance=0.0

        System.out.println("transfer 1000 money from b1 to b2");
        b1.transfer(1000, b2);
        System.out.println("b1: " + b1); // b1: P balance=1010.0
        System.out.println("b2: " + b2); // b2: K balance=1010.0

        BankAccount c1 = new CheckingAccount("Checking1", 1000, 500);
        BankAccount c2 = new CheckingAccount("Checking2", 1000, 500);
        c1.withdraw(700); // CheckingAccount::withdraw Cannot be withdrawn due to overdraftLimit
        c2.withdraw(800); // CheckingAccount::withdraw Cannot be withdrawn due to overdraftLimit
        c1.print(); // CheckingAccount: Checking1 balance=1020.0
        c2.print(); // CheckingAccount: Checking1 balance=1020.0

        BankAccount s1 = new SavingAccount("Saving1", 1000);
        s1.deposit(5000);
        s1.withdraw(1000);
        s1.print(); // SavingAccount: Saving1 balance=5250.0

        BankAccount s2 = new SavingAccount("Saving2", 1000);
        s2.withdraw(2000); // SavingAccount::withdraw Amount is larger than current balance.
        s2.print(); // SavingAccount: Saving2 balance=1050.0
    }
}