在声明中包含abstract关键字的类称为抽象类。
示例
本节为您提供了抽象类的示例。要创建抽象类,只需在类声明中的 class 关键字之前使用abstract 关键字即可。
/* File name : 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; } }
您可以观察到,除了抽象方法之外,Employee 类与 Java 中的普通类相同。该类现在是抽象的,但它仍然具有三个字段、七个方法和一个构造函数。
现在您可以尝试通过以下方式实例化 Employee 类 -
/* File name : AbstractDemo.java */ public class AbstractDemo { public static void main(String [] args) { /* Following is not allowed and would raise error */ Employee e = new Employee("George W.", "Houston, TX", 43); System.out.println("\n Call mailCheck using Employee reference--"); e.mailCheck(); } }
当你编译上面的类时,它会给出以下错误 -
Employee.java:46: Employee is abstract; cannot be instantiated Employee e = new Employee("George W.", "Houston, TX", 43); ^ 1 error
以上是在Java中的抽象类的详细内容。更多信息请关注PHP中文网其他相关文章!