<?php

interface ia {
    const c = 'Sea';
}

class Foo implements ia {
	
	// const c = "Lake";  
	
	// Attempting to override ia's constant c in
	// this class triggers a fatal error.
	
}

class FooBar extends Foo implements ia {
	
	const c = 'Ocean'; // No error, class constant
	 		   // overriding ia's definition.
	
	public function show(){
		// ia's definition is still accessible.
	  return ia::c;
	}
}

$i = new FooBar;
echo FooBar::c;
echo $i->show();

?>

OceanSea