New Features:
- Assertion(jdk-4)
- For-each loop(jdk-5)
- Varargs(jdk-5)
- Static Import(jdk-5)
- Autoboxing and Unboxing(jdk-5)
- Enum Type(jdk-5)
- Generics(jdk-5)
- Annotation(jdk-5)
- String datatype in switch(jdk-7)
- Parameterized try(jdk-7)
- Catch with multiple parameters(jdk-7)
- Nio pacakge(jdk-7)
- Underscores in number(jdk-7)
.................
Assertion:
Comes in jdk 1.4.
Assertions are of two types:1) Preconditions 2) Postconditions.
Assertions is used to make java-program more understandable and user
friendly, because assertions can be used while defining preconditions and post
conditions of the program. Apart from this assertions can use on
internal, control flow and class invariants as well to improve the programming
experience.
Assertion statements have two form-
assert expression;This statement evaluates expression and throws an AssertionError if the expression is false.
To enable assertions at runtime, -ea command-line option is used
Preconditions are the assertions which invokes when a method is
invoked and Postconditions are the assertions which invokes
after a method finishes.
Where to use Assertions
Declaring Assertion:
assert expression1 : expression2
This statement evaluates
expression1 and throws an AssertionError with expression2 as the error message
if expression1 is false.
In the above example, When the
user enters the number scanner.nextInt() method reads the number from the
command line. The assert statement determines whether the entered number is within the valid range. If the user
entered a number which is out of range then the error occurs.
Example:
import java.util.*;
class AssertionTest
{
public
static void main( String args[] )
{
Scanner scanner =
new Scanner( System.in );
System.out.print("Enter your age ");
int
value = scanner.nextInt();
assert
value>=18:" Not valid,Only within 18 is allowed.";
System.out.println("value
is "+value);
}
}
To run the above example,
Compile the example with: javac AssertionTest.java
Run the example with: java -ea AssertionTest
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