Question

I know C/C++/C#/ActionScript/PHP and have worked in all of them. As per my Knowledge we generally initialize object as

Object obj = new Object();

Java does the same most of the times but yesterday while working with Netbeans and JTable swing control, IDE generated this code which kind of looks a bit strange to me. Any explanation of how is it initializing an object? What’s the {..} part after new DefaultTableModel(..)?

_model = new DefaultTableModel(
     new Object [][] {
     },
     new String [] {
         "Id", "Project Title", "Start Date", "Deadline", "Description", "PercentDone"
     }) {
         Class[] types = new Class [] {
             java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class
         };
         boolean[] canEdit = new boolean [] {
             false, false, false, false, false, false
         };

         @Override
         public Class getColumnClass(int columnIndex) {
              return types [columnIndex];
         }

         @Override
         public boolean isCellEditable(int rowIndex, int columnIndex) {
             return canEdit [columnIndex];
         }
     };

Answer 1

It’s called an anonymous class, combining class definition and instantiation. Links:

• http://mindprod.com/jgloss/anonymousclasses.html
• http://docstore.mik.ua/orelly/java-ent/jnut/ch03_12.htm
• http://en.wikibooks.org/wiki/Java_Programming/Nested_Classes#Anonymous_Classes
• Is usage of anonymous classes in Java considered bad style or good?

---

Line by line explanation:

// creates a new instance of the DefaultTableModel class and assigns it
// to a previously declared variable named _model.
// Note that contrary to C++, starting a variable name with an underscore is
// legal but discouraged as a convention in Java
// (http://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html)
_model = new DefaultTableModel(

    // this is first parameter to the DefaultTableModel constructor taking
    // a two-dimensional array of Objects as the first parameter, and an
    // array of Objects as the second. This creates an empty 2D array.
    new Object [][] {
    },

    // this is the second parameter to the DefaultTableModel constructor.
    // It creates an array of Strings initialized with the provided values
    new String [] {
        "Id", "Project Title", "Start Date", "Deadline", "Description", "PercentDone"
    })

        // start of the redifinition of the DefaultTableModel class
        {

            // creates a member variable named types at the default visibility.
            // This member is an array of Class objects, initialized with the
            // provided values
            Class[] types = new Class [] 
                java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class
            };

            // creates a member variable named canEdit at the default visibility.
            // This member is an array of booleans, all initialized to false.
            boolean[] canEdit = new boolean [] {
                false, false, false, false, false, false
            };

            // annotation used by IDEs and the compiler specifying that the
            // method that follows overrides a method in the DefaultTableModel
            // class. If the methods does not actually override such a method,
            // an error will be generated (e.g. due to a spelling mistake in the
            // method name or the wrong parameters being declared)
            @Override

            // override of the default getColumnClass method
            public Class getColumnClass(int columnIndex) {
                return types [columnIndex];
            }

            // see explanation above
            @Override

            // override of the default isCellEditable method
            public boolean isCellEditable(int rowIndex, int columnIndex) {
                return canEdit [columnIndex];
            }

    // end of the anonymous class
    };
// end of the constructor call and assignment to _model statement.
);