Collections

-Contains no duplicate elements.

-Can contain at most one Null value.

-Elements are not key-value pairs.

-Accessing an element can be almost as fast as performing a similar operation on an array.

Which of these classes provides the specified features?

• LinkedList

• TreeMap

• HashSet

• LinkedHashMap

• HashMap

Which of the following statement about Set is true?

• A HashSet cannot have a null value.

• Set allows duplicate values.

• Set allows null values but only single occurrence.

• Set extends the Java.util.collection interface.

• {1=C, 2=JavaEE, 4=Python, 3=PHP}

• {1=C, 2=JavaSE, 3=Python, 4=PHP}

• {1=C, 2=JavaEE, 3=Python, 4=PHP}

• {1=C, 2=JavaSE,2=JavaEE, 3=Python, 4=PHP}

• NullPointerException

• {null=null, a=null, b=JavaSE, c=PHP, d=Python}

• {a=null, b=JavaSE, c=PHP, d=Python}

• {b=JavaSE, c=PHP, d=Python}

• Compilation Fails

• 4

• 5

• 6

• 12

-Entries are not organized as key/value pairs.

-Duplicate entries are rejected.

Which interface of the java.util package offers the specified behavior?

• List

• Map

• Set

• None of the above

• [Computer, Network, Networks, Programming, Security]

• [Computer, Programming, Network, Networks, Programming, Security]

• [Computer, Programming, Computer, Networks, Network, Security]

• [Computer, Networks, Network, Programming, Security]

Which of the following is/are correct statements?

• HashSet class implements the Set interface

• HashSet does not allow duplicate elements that means you can not store duplicate values in HashSet.

• HashSet permits to have a single null value.

• HashMap does not allow duplicate keys however it allows to have duplicate values.

• HashMap and HashSet are threadsafe

List listNames = new ArrayList();

listNames.add("Tom");

listNames.add("Mary");

listNames.add("Peter");

String name2 = (String) listNames.get(1);

System.out.println(name2);

What is the output of the above code

• Tom

• Mary

• Peter

• raises Exception

Which of the following statement is not True about Generics in java?

• Generics are features of the Java programming language that allow programmers to write parameterized code.

• With generics, the compiler can not detect violations at compile time, thus eliminating potential bugs.

• Due to the demand of safer code, generics were added to the Java programming language.

• generics allow you to write generic code

• Stronger type checks at compile time