Editing Java syntax (section)

=====Abstract classes=====

An [http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.1.1.1   Abstract Class] is a class that is incomplete, or is to be considered incomplete, so cannot be instantiated.

A class C has abstract methods if any of the following is true:

* C explicitly contains a declaration of an abstract method.
* Any of C's superclasses has an abstract method and C neither declares nor inherits a method that implements it.
* A direct superinterface of C declares or inherits a method (which is therefore necessarily abstract) and C neither declares nor inherits a method that implements it.
* A subclass of an abstract class that is not itself abstract may be instantiated, resulting in the execution of a constructor for the abstract class and, therefore, the execution of the field initializers for instance variables of that class.

<syntaxhighlight lang="java">
package org.dwwwp.test;

/**
 * @author jcrypto
 */
public class AbstractClass {
    private static final String hello;

    static {
        System.out.println(AbstractClass.class.getName() + ": static block runtime");
        hello = "hello from " + AbstractClass.class.getName();
    }

    {
        System.out.println(AbstractClass.class.getName() + ": instance block runtime");
    }

    public AbstractClass() {
        System.out.println(AbstractClass.class.getName() + ": constructor runtime");
    }

    public static void hello() {
        System.out.println(hello);
    }
}
</syntaxhighlight>
<syntaxhighlight lang="java">
package org.dwwwp.test;

/**
 * @author jcrypto
 */
public class CustomClass extends AbstractClass {

    static {
        System.out.println(CustomClass.class.getName() + ": static block runtime");
    }

    {
        System.out.println(CustomClass.class.getName() + ": instance block runtime");
    }

    public CustomClass() {
        System.out.println(CustomClass.class.getName() + ": constructor runtime");
    }

    public static void main(String[] args) {
        CustomClass nc = new CustomClass();
        hello();
        //AbstractClass.hello();//also valid
    }
}
</syntaxhighlight>

Output:
<syntaxhighlight lang="text">
org.dwwwp.test.AbstractClass: static block runtime
org.dwwwp.test.CustomClass: static block runtime
org.dwwwp.test.AbstractClass: instance block runtime
org.dwwwp.test.AbstractClass: constructor runtime
org.dwwwp.test.CustomClass: instance block runtime
org.dwwwp.test.CustomClass: constructor runtime
hello from org.dwwwp.test.AbstractClass
</syntaxhighlight>