Tag: java

Questions Related to java

HashMap is thread-safe whereas Hashtable is not10, Which of the following assignment statements is invalid?
java

  1. double D = 45456.444;

  2. long L = 45784;

  3. int I = L;

  4. int J = (int) D;

Show answer
Correct Option: C

Assume the following method is properly synchronized and called from a thread A on an object B: wait(2000); After calling this method, when will the thread A become a candidate to get another turn at the CPU?

java

  1. After object B is notified, or after two seconds

  2. After the lock on B is released, or after two seconds

  3. Two seconds after object B is notified

  4. Two seconds after lock B is released.

Show answer
Correct Option: A

for(Object obj: expression) { } What interface must the ?expression? implement in order for you to use it with enhanced for loop construct?

java

  1. Iterator

  2. Map

  3. Enumeration

  4. Iterable

Show answer
Correct Option: D

Given:

TreeSet map = new TreeSet();
 map.add("one");
 map.add("two");
 map.add("three");
 map.add("four"};
 map.add("one");
 Iterator it = map.iterator();
 while (it.hasNext() ) {
 System.out.print( it.next() + " " );
 }
java

  1. Compilation fails

  2. one two three four

  3. four three two one

  4. four one three two

  5. one two three four one

  6. one four three two one

Show answer
Correct Option: D

Which is true about a method-local inner class?
java

  1. It must be marked final

  2. It can be marked abstract

  3. It can be marked public

  4. It can be marked static

Show answer
Correct Option: B

Which is true about an anonymous inner class?
java

  1. It can extend exactly one class and implement exactly one interface

  2. It can extend exactly one class and can implement multiple interfaces

  3. It can extend exactly one class or implement exactly one interface

  4. It can implement multiple interfaces regardless of whether it also extends a class

  5. It can implement multiple interfaces if it does not extend a class

Show answer
Correct Option: C

Which is true?
java

  1. The java command can access classes from more than one package, from a single JAR file.

  2. JAR files can be used with the java command but not with the javac command.

  3. In order for JAR files to be used by java, they MUST be placed in the /jre/lib/ext sub-directory within the J2SE directory tree.

  4. When a part of a directory tree that includes subdirectories with files is put into a JAR file, all of the files are saved in the JAR file, but the subdirectory structure is lost.

Show answer
Correct Option: A

Which of the following statement is true?
java

  1. X extends Y is correct if and only if X is a class and Y is an interface

  2. X extends Y is correct if and only if X is an interface and Y is a class

  3. X extends Y is correct if X and Y are either both classes or both interfaces

  4. X extends Y is correct for all combinations of X and Y being classes and/or interfaces.

Show answer
Correct Option: C

Select a statement that best indicate a situation with low coupling.
java

  1. The attributes of the class are all private

  2. The class refers to a small number of other objects

  3. The object contains only a small number of variables

  4. The object is referred to using an anonymous variable, not directly

  5. The reference variable is declared for an interface type, not a class. The interface provides a small number of methods

Show answer
Correct Option: E

Applications in a J2EE architecture

java

  1. must be created via a Java IDE.

  2. can run on different machines, but only with the same Operating System.

  3. are typically based on Servlets, JSPs and Enterprise Java Beans.

  4. need no runtime environment.

Show answer
Correct Option: C

AI Explanation

To answer this question, we need to understand the key components and architecture of a J2EE (Java 2 Enterprise Edition) application.

Option A) "must be created via a Java IDE" - This option is incorrect because J2EE applications can be developed using any text editor or Integrated Development Environment (IDE) that supports Java development. While a Java IDE can provide features and tools to streamline the development process, it is not a requirement for creating J2EE applications.

Option B) "can run on different machines, but only with the same Operating System" - This option is incorrect because J2EE applications are designed to be platform-independent. They can run on different machines with different operating systems as long as the Java Virtual Machine (JVM) is installed on the target machine. This allows the J2EE application to be deployed and run on various platforms, such as Windows, Linux, or macOS.

Option C) "are typically based on Servlets, JSPs, and Enterprise Java Beans" - This option is correct because J2EE applications are commonly built using a combination of Servlets, JavaServer Pages (JSPs), and Enterprise Java Beans (EJBs). Servlets handle the request-response cycle, JSPs provide the presentation layer, and EJBs handle the business logic and data persistence.

Option D) "need no runtime environment" - This option is incorrect because J2EE applications require a runtime environment to execute. The J2EE runtime environment, also known as an application server or container, provides the necessary infrastructure and services for the application to run, such as managing components, handling transactions, and providing security.

Therefore, the correct answer is C) J2EE applications are typically based on Servlets, JSPs, and Enterprise Java Beans. These components work together to create a scalable and robust architecture for building enterprise-level applications.