SCJP exercise : enum

Exercise :

public class Test {

enum Animal { "CATS", "DOGS", "ELEPHANT"};
public static void main(String [] args) {

Animal myAnimal = Animal.CATS;
if ( myAnimal == Animal.CATS) {
System.out.println("It's a CATS");
} else if (myAnimal.equals(Animal.DOGS)) {
System.out.println("It's a DOGS");
} else {
System.out.println("It's an elephant");
}
}

}


What is the result ? (choose one)

A It's a CATS
B It's a DOGS
C It's an elephant
D Compilation fails
E An exception is thrown at runtime




Solution :

The solution is D.There is an compilation error because the enum syntax is wrong.
It should be : enum Animal { CATS, DOGS, ELEPHANT};

SCJP exercise : enum

Exercise :



Given the following :
public class Test {

enum Animal { CATS, DOGS, ELEPHANT};
public static void main(String [] args) {

Animal myAnimal = Animal.CATS;
if ( myAnimal == Animal.CATS) {
System.out.println("It's a CATS");
} else if (myAnimal.equals(Animal.DOGS)) {
System.out.println("It's a DOGS");
} else {
System.out.println("It's an elephant");
}
}

}


What is the result ? (choose one)

A It's a CATS
B It's a DOGS
C It's an elephant
D Compilation fails
E An exception is thrown at runtime





Solution :

The solution is A.There is no errors.You can use enum with == or with the method equals.

SCJP exercise : operators

Exercise :



Given the following :
public class Test {


public static void main(String [] args) {

int num = 1;
if ( num == 'a') {
System.out.println("Good result !");
} else {
System.out.println("Result:" + num);
}
}

}


What is the result ? (choose one)

A Good result !
B Result:1
C Compilation fails
D An exception is thrown at runtime





Solution :

The result is C.There is no compilation error.You can compare 1 with 'a' because the comparison use the unicode value of a.So it's correct to compare 1 with 'a'.

SCJP exercise : operators

An other exercise ! The goal is practice and learn commons java certification SCJP questions.

Exercise :



Given the following :
public class Test {
public static void main(String [] args) {

int num = 1;
if ( num = 2) {
System.out.println("Result:" + num);
}
System.out.println("Result:" + num);
}
}


What is the result ? (choose one)

A Result:1
B Result:2
C Compilation fails
D An exception is thrown at runtime





Solution :

The solution is C.In fact we set num to 2 with num=2.
So the result of the setting is an int.Or the if is waiting a boolean so the compilation fails.

Good year

Hi !

This year we will see many things like certification exercise, Java tips, Go langage ...
So it's exiting !

GWT [ERROR] No source code is available for ...GWTTestCase

Problem :


You have the following error:
[ERROR] Line 11: No source code is available for type com.google.gwt.junit.client.GWTTestCase;
did you forget to inherit a required module?


Solution :

In your module file(*.gwt.xml), simply add :
"< name="com.google.gwt.junit.JUnit">"

Eclipse GWT_EXTERNAL_BROWSER

Problem :


When you compile in hosted mode, you have the following error :
[ERROR] Unable to find a default external web browser
[WARN] Try setting the environment variable GWT_EXTERNAL_BROWSER to your web browser executable before launching the GWT shell


Solution :

In eclipse, Go on Run -> Run Configurations.Then, choose your google's project and click on Environment.The last thing, you have to do is to add the variable GWT_EXTERNAL_BROWSER with the value firefox.