What is difference between Unchecked and Checked Exceptions? and What is difference between Synchronized method and Synchronized block?

What is difference between Unchecked and Checked Exceptions?

Unchecked exceptions :

• represent defects in the program (bugs) - often invalid arguments passed to a non-private method. To quote from The Java Programming Language, by Gosling, Arnold, and Holmes : "Unchecked runtime exceptions represent conditions that, generally speaking, reflect errors in your program's logic and cannot be reasonably recovered from at run time."
• are subclasses of RuntimeException, and are usually implemented using IllegalArgumentException, NullPointerException, or IllegalStateException
• a method is not obliged to establish a policy for the unchecked exceptions thrown by its implementation (and they almost always do not do so)

Checked exceptions :

• represent invalid conditions in areas outside the immediate control of the program (invalid user input, database problems, network outages, absent files)
• are subclasses of Exception
• a method is obliged to establish a policy for all checked exceptions thrown by its implementation (either pass the checked exception further up the stack, or handle it somehow)

What is difference between Synchronized method and Synchronized block?

What is difference between Synchronized method and Synchronized block?

The key difference is this: if you declare a method to be synchronized, then the entire body of the method becomes synchronized; if you use the synchronized block, however, then you can surround just the "critical section" of the method in the synchronized block, while leaving the rest of the method out of the block.
If the entire method is part of the critical section, then there effectively is no difference. If that is not the case, then you should use a synchronized block around just the critical section. The more statements you have in a synchronized block, the less overall parallelism you get, so you want to keep those to the minimum.

What is difference between ArrayList and Vector ?

1. The Vector class is synchronized, the ArrayList is not.
2. ArrayList is fast than the Vector.