An abstract class can have abstract methods.
even if it contains no abstract methods. method of the subclass. This Java abstract class tutorial explains how abstract classes are created in Java, what rules superclass. Here Subclasses only need to worry about processing the data from the InputStream passed to the class can have a mixture of abstract and non-abstract methods.
methods of the superclass are just inherited as they are. You could have just used an In that case, you cannot make the method abstract. 
Just like methods in a processURLData() method.
The purpose of abstract classes is to function as base classes which can be extended by subclasses An abstract Here is an example subclass of the abstract class MyAbstractClass: Notice how MySubClass has to implement the abstract method abstractMethod() from its abstract superclass This tutorial gets into the purpose of abstract classes in Java in more detail towards the For instance, imagine that a certain process requires 3 steps: If the steps before and after the action are always the same, the 3-step process could be implemented in an The rest of the code is inherited from the URLProcessorBase superclass. Thus, the following Java code is no longer valid: If you try to compile the code above the Java compiler will generate an error, saying that you cannot instantiate
ordinary class.
The above example did not have a default implementation for the action() method. end of this text. apply to them. abstract superclass with this Java code: Notice how the action() method is abstract. declaration. override. to create a full implementation. class for a subclass, and that the abstract method should be implemented in the subclass. Jakob Jenkov Of course, the MyAbstractProcess did not have to be an abstract class to function as a base 
Subclasses of MyAbstractProcess Subclasses of URLProcessorBase abstract class can process data downloaded from URLs without worrying about clearly to users of this class that this class should not be used as it is. This method in turn calls the processURLData() in the URLProcessorImpl class. It just has a method signature. of its abstract superclass. adding the abstract keyword in front of the method declaration. The purpose of an abstract class is to function as a base for the stepBefore() and stepAfter() of the abstract superclass, and the action() The non-abstract The Template Method design pattern provides a partial implementation You can still make the superclass abstract though, subclasses. They can also be overridden, if needed. Last update: 2015-03-09. This is done by the URLProcessorBase.
Here is an example of how to use the URLProcessorImpl class: The process() method is called, which is implemented in the URLProcessorBase Instead it should be used as a base The only time a subclass of an abstract class is not forced to implement all abstract methods of its superclass, method because it is an abstract method. When the process() method of the subclass is called, the full process is executed, including Subclasses of URLProcessorBase have to implement the processURLData() an abstract class. of some process, which subclasses can complete when extending the Template Method base class. Not all methods in an abstract class have to be abstract methods. MyAbstractClass because it is an abstract class. Notice how the subclass only implements the processURLData() method, and nothing A Java abstract class is a class which cannot be instantiated, meaning you cannot create new Subclasses of an abstract class must implement (override) all abstract methods The example I showed you above with the URLProcessorBase class is actually an example Here is a Java abstract class example: That is all there is to declaring an abstract class in Java. Now you cannot create instances of instances of an abstract class. Notice how the processURLData() is an abstract method, and that URLProcessorBase is This makes it easier to implement classes that processes data from URLs. your superclass might actually have a default implementation for the method that subclasses are supposed to MyAbstractClass. Nor did the action() method have to be abstract either. is if the subclass is also an abstract class. is a Java abstract method example: An abstract method has no implementation. class. of the Template Method design pattern. can now extend MyAbstractProcess and just override the action() method. You declare a method abstract by more. MyAbstractClass. Java interface. Here is a more concrete example that opens a URL, processes it and closes the connection to the URL afterwards. Java Project Overview, Compilation and Execution, Abstract Classes and the Template Method Design Pattern. In some cases
However, by making the method to implement abstract, and thus the class too, you signal opening and closing the network connection to the URL. If a class has an abstract method, the whole class must be declared abstract. In Java you declare that a class is abstract by adding the abstract keyword to the class
even if it contains no abstract methods. method of the subclass. This Java abstract class tutorial explains how abstract classes are created in Java, what rules superclass. Here Subclasses only need to worry about processing the data from the InputStream passed to the class can have a mixture of abstract and non-abstract methods.
methods of the superclass are just inherited as they are. You could have just used an In that case, you cannot make the method abstract. Just like methods in a processURLData() method. The purpose of abstract classes is to function as base classes which can be extended by subclasses An abstract Here is an example subclass of the abstract class MyAbstractClass: Notice how MySubClass has to implement the abstract method abstractMethod() from its abstract superclass This tutorial gets into the purpose of abstract classes in Java in more detail towards the For instance, imagine that a certain process requires 3 steps: If the steps before and after the action are always the same, the 3-step process could be implemented in an The rest of the code is inherited from the URLProcessorBase superclass. Thus, the following Java code is no longer valid: If you try to compile the code above the Java compiler will generate an error, saying that you cannot instantiate
ordinary class.
The above example did not have a default implementation for the action() method. end of this text. apply to them. abstract superclass with this Java code: Notice how the action() method is abstract. declaration. override. to create a full implementation. class for a subclass, and that the abstract method should be implemented in the subclass. Jakob Jenkov Of course, the MyAbstractProcess did not have to be an abstract class to function as a base Subclasses of MyAbstractProcess Subclasses of URLProcessorBase abstract class can process data downloaded from URLs without worrying about clearly to users of this class that this class should not be used as it is. This method in turn calls the processURLData() in the URLProcessorImpl class. It just has a method signature. of its abstract superclass. adding the abstract keyword in front of the method declaration. The purpose of an abstract class is to function as a base for the stepBefore() and stepAfter() of the abstract superclass, and the action() The non-abstract The Template Method design pattern provides a partial implementation You can still make the superclass abstract though, subclasses. They can also be overridden, if needed. Last update: 2015-03-09. This is done by the URLProcessorBase. Here is an example of how to use the URLProcessorImpl class: The process() method is called, which is implemented in the URLProcessorBase Instead it should be used as a base The only time a subclass of an abstract class is not forced to implement all abstract methods of its superclass, method because it is an abstract method. When the process() method of the subclass is called, the full process is executed, including Subclasses of URLProcessorBase have to implement the processURLData() an abstract class. of some process, which subclasses can complete when extending the Template Method base class. Not all methods in an abstract class have to be abstract methods. MyAbstractClass because it is an abstract class. Notice how the subclass only implements the processURLData() method, and nothing A Java abstract class is a class which cannot be instantiated, meaning you cannot create new Subclasses of an abstract class must implement (override) all abstract methods The example I showed you above with the URLProcessorBase class is actually an example Here is a Java abstract class example: That is all there is to declaring an abstract class in Java. Now you cannot create instances of instances of an abstract class. Notice how the processURLData() is an abstract method, and that URLProcessorBase is This makes it easier to implement classes that processes data from URLs. your superclass might actually have a default implementation for the method that subclasses are supposed to MyAbstractClass. Nor did the action() method have to be abstract either. is if the subclass is also an abstract class. is a Java abstract method example: An abstract method has no implementation. class. of the Template Method design pattern. can now extend MyAbstractProcess and just override the action() method. You declare a method abstract by more. MyAbstractClass. Java interface. Here is a more concrete example that opens a URL, processes it and closes the connection to the URL afterwards. Java Project Overview, Compilation and Execution, Abstract Classes and the Template Method Design Pattern. In some cases
However, by making the method to implement abstract, and thus the class too, you signal opening and closing the network connection to the URL. If a class has an abstract method, the whole class must be declared abstract. In Java you declare that a class is abstract by adding the abstract keyword to the class