Method Chaining question

[Saeed Amer]

Hi there

I am almost 100% sure that method-chanining is supported in Java. I said "almost" because following chaining doesn't compile.

Here is the original piece of code:

    	 GregorianCalendar gc = new GregorianCalendar();
    	 gc.set(year, month, start + 2, 9, 0, 0);
    	 Date dt = new Date(gc.getTimeInMillis());

I wanted to do something like this:

    	 GregorianCalendar gc = new GregorianCalendar();
    	 Date dt = new Date(gc.set(year, month, start + 2, 9, 0, 0)
                              .getTimeInMillis()
                            );

but this code doesn't compile.

OR in other words, why can't I do the following:

    	 long longValue = new GregorianCalendar().set(year, month, start + 2, 9, 0, 0)
    	                                         .getTimeInMillis();

Could someone please elaborate the concept why Java compiler is not allowing to do this?

Regards,

Saeed

[Henry Wong]

Could someone please elaborate the concept why Java compiler is not allowing to do this?

When you say this...

long longValue = new GregorianCalendar().set(year, month, start + 2, 9, 0, 0)   
                                                 .getTimeInMillis();  

The compiler reads it as this...

long longValue = (new GregorianCalendar().set(year, month, start + 2, 9, 0, 0))   
                                                 .getTimeInMillis();  

Basically, you are asking the compiler to create a new GregorianCalendar object; using that object, call the set() method; and using whatever is returned from the set() method, call the getTimeInMillis() method. Since the set() method does actually return anything -- you can't dereference it to get to the getTimeInMillis() method.

If the set() method returns a copy of the original object -- like the methods of the StringBuffer class -- you can chain the methods.

Henry

[Saeed Amer]

Great - thank you for so simple explanation.

Regards,
Saeed