How to define an abstract method in Java

In Java, the abstract keyword is used to define abstract methods. Abstract methods are methods without an implementation, only containing the method declaration without a method body. Abstract methods must be defined in an abstract class, which also needs to be marked with the abstract keyword. The syntax for defining abstract methods is as follows:

public abstract class AbstractClass {
    public abstract void abstractMethod();
}

In the given example, AbstractClass is an abstract class that defines an abstract method abstractMethod(). When a subclass inherits this abstract class, it must implement the abstract method, otherwise the subclass must also be declared as an abstract class.