私有实例变量和公共方法

public class Main {

  public static void main(String[] args) {

    MyCredit ac = new MyCredit();

    double balance = ac.getBalance();/**from n o w  j a v a  . c o m**/

    System.out.println("Balance = " + balance);


    ac.credit(24.718);

    ac.debit(10.112);


    balance = ac.getBalance();

    System.out.println("Balance = " + balance);


    // Attempt to credit and debit invalid amounts

    ac.credit(-24.90);

    ac.debit(Double.POSITIVE_INFINITY);


    balance = ac.getBalance();

    System.out.println("Balance = " + balance);


    // Attempt to debit more than the balance

    ac.debit(200.00);
// from N o w J a v a . c o m - 时代Java

    balance = ac.getBalance();

    System.out.println("Balance = " + balance);

  }

}


class MyCredit {

  private double balance;

  // Return the balance of this account

  public double getBalance() {

    return this.balance;

  }


  public int credit(double amount) {

    if (amount < 0.0 || Double.isNaN(amount) || Double.isInfinite(amount)) {

      System.out.println("Invalid credit amount: " + amount);

      return -1;

    }

    System.out.println("Crediting amount: " + amount);

    this.balance = this.balance + amount;

    return 1;

  }


  public int debit(double amount) {

    if (amount < 0.0 || Double.isNaN(amount) || Double.isInfinite(amount)) {

      System.out.println("Invalid debit amount: " + amount);

      return -1;

    }