How to define an abstract class in Java?

In Java, abstract classes can be defined using the keyword abstract. Abstract classes are classes that cannot be instantiated and are primarily used for inheritance by other classes. The syntax for defining an abstract class is as follows:

public abstract class ClassName {
    // 抽象类的成员变量、成员方法和构造方法的定义
}

It is important to note that abstract classes can contain member variables, member methods, and constructors, but the abstract class itself cannot be instantiated. If a class inherits from an abstract class, then that class must implement all the abstract methods in the abstract class, unless the class itself is also an abstract class.

An abstract method refers to only having the declaration of the method, without the implementation of the method. The definition of an abstract method is as follows:

public abstract void methodName();

It is important to note that abstract methods must be defined in an abstract class. An abstract class can contain zero or more abstract methods.

To sum up, the steps for defining an abstract class are as follows:

1. summary
2. Define member variables, member methods, and constructors in abstract class.
3. summary
4. Other classes can inherit abstract classes and implement their abstract methods.