Suppose you will fill a glass with ice cubes. When the ice cubes melt, is the glass still full

No. It will not still be full. The reason being is because when it melts, it's almost the same thing as compacting things down into another object (container). Therefore, you will have some room left i the glass. Like, if your trashcan was over-flowing, and you push it down to compact it so you can add more trash. So when the ice melts, it will not be full.