Core Java Questions et reponses d'entretien
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Question 206. What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.
Question 207. What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
Question 208. What are E and PI?
E is the base of the natural logarithm and PI is mathematical value pi.
Question 209. What happens when you add a double value to a String?
The result is a String object.
Question 210. Why can't I say just abs() or sin() instead of Math.abs() and Math.sin()?
The import statement does not bring methods into your local name space. It lets you abbreviate class names, but not get rid of them altogether. That's just the way it works, you'll get used to it. It's really a lot safer this way.
However, there is actually a little trick you can use in some cases that gets you what you want. If your top-level class doesn't need to inherit from anything else, make it inherit from java.lang.Math. That *does* bring all the methods into your local name space. But you can't use this trick in an applet, because you have to inherit from java.awt.Applet. And actually, you can't use it on java.lang.Math at all, because Math is a '??final'?? class which means it can't be extended.
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Les plus utiles selon les utilisateurs :
- How could Java classes direct program messages to the system console, but error messages, say to a file?
- What are the differences between an interface and an abstract class?
- Why would you use a synchronized block vs. synchronized method?
- How can you force garbage collection?
- What are the differences between the methods sleep() and wait()?