java unchecked exceptions

1//pErrors and RuntimeExceptions are unchecked — that is, the compiler does not enforce (check) that you handle them explicitly. 
2Methods do not have to declare that they throw them (in the method signatures). 
3It is assumed that the application cannot do anything to recover from these exceptions (at runtime). 
4Example
5If you have declared an array of size 5 in your program, and trying to call the 6th element of the array then an ArrayIndexOutOfBoundsException occurs. 
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7public class Unchecked_Demo {
8   
9   public static void main(String args[]) {
10      int num[] = {1, 2, 3, 4};
11      System.out.println(num[5]);
12   }
13}
14Errors
15These are not exceptions at all, but problems that arise beyond the control of the user or the programmer. Errors are typically ignored in your code because you can rarely do anything about an error. For example, if a stack overflow occurs, an error will arise. They are also ignored at the time of compilation. 
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17Exception Hierarchy
18 All exception classes are subtypes of the java.lang.Exception class. The exception class is a subclass of the Throwable class. Other than the exception class there is another subclass called Error which is derived from the Throwable class. 
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