In this JUnit Tutorial in java we will learn what is assert keyword in java? What are advantages of using assertions keyword in java junit ?
- Assertions makes our code easy to debug at runtime in java.
- Assertions makes our code production ready.
Before writing programs to use assert you must know : How to enable Assertions - assert keyword in eclipse in java
Program to use use Assertions - assert keyword in java junit >
public class AssertionsExample {
public static void main(String args[]) {
String str = null;
assert (str != null);
System.out.println(str.charAt(0));
}
}
/*OUTPUT
Exception in thread "main" java.lang.AssertionError
At AssertionsExample.main(AssertionsExample.java:4)
*/
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To avoid NullPointerException at line 5 you must use assert before that.
Use assertEquals method in java junit >
assertEquals() - Method compares the two objects for equality.
assertEquals() method internally uses the equals() method to determine equality of the passed objects in the method.
import static org.junit.Assert.assertEquals;
public class AssertionsEqualExample {
public static void main(String args[]) {
String str1 = new String("ab");
String str2 = new String("ab");
assertEquals(str1, str2);
System.out.println("after assertEquals");
}
}
/*OUTPUT
after assertEquals
*/
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Use assertTrue and assertFalse() method in java junit>
assertTrue() - Method tests whether a value returned is true.
assertFalse() - Method tests whether a value returned is false
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
public class AssertionsTrueFalseExample {
public static void main(String args[]) {
String str1 = new String("ab");
String str2 = new String("ab");
assertTrue(str1.equals(str2));
System.out.println("after assertTrue");
assertFalse(!str1.equals(str2));
System.out.println("after assertFalse");
}
}
/*OUTPUT
after assertTrue
after assertFalse
*/
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Jar used in above program > junit-4.8.2.jar
So in this JUnit Tutorial in java we learned what is assert keyword in java. And advantages of using assertions keyword in java junit.
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