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在Java語(yǔ)言中使用abstract class來(lái)定義抽象類(lèi)。如下實(shí)例：

/* 文件名 : Employee.java */
public abstract class Employee
{
   private String name;
   private String address;
   private int number;
   public Employee(String name, String address, int number)
   {
      System.out.println("Constructing an Employee");
      this.name = name;
      this.address = address;
      this.number = number;
   }
   public double computePay()
   {
     System.out.println("Inside Employee computePay");
     return 0.0;
   }
   public void mailCheck()
   {
      System.out.println("Mailing a check to " + this.name
       + " " + this.address);
   }
   public String toString()
   {
      return name + " " + address + " " + number;
   }
   public String getName()
   {
      return name;
   }
   public String getAddress()
   {
      return address;
   }
   public void setAddress(String newAddress)
   {
      address = newAddress;
   }
   public int getNumber()
   {
     return number;
   }
}

注意到該Employee類(lèi)沒(méi)有什么不同，盡管該類(lèi)是抽象類(lèi)，但是它仍然有3個(gè)成員變量，7個(gè)成員方法和1個(gè)構(gòu)造方法。 現(xiàn)在如果你嘗試如下的例子：

/* 文件名 : AbstractDemo.java */
public class AbstractDemo
{
   public static void main(String [] args)
   {
      /* 以下是不允許的，會(huì)引發(fā)錯(cuò)誤 */
      Employee e = new Employee("George W.", "Houston, TX", 43);

      System.out.println("\n Call mailCheck using Employee reference--");
      e.mailCheck();
    }
}

當(dāng)你嘗試編譯AbstractDemo類(lèi)時(shí)，會(huì)產(chǎn)生如下錯(cuò)誤：

Employee.java:46: Employee is abstract; cannot be instantiated
      Employee e = new Employee("George W.", "Houston, TX", 43);
                   ^
1 error