Midterm questions

Question 1

Normally the instance variables in a java class are given which access qualifier?

Answer 1

private

Question 2

A data item that can only be used within in java method is called?

Answer 2

local variable

Question 3

suppose that java class A inherits from Class B, and suppose a1 and b1 refer to objects of class A and B. Which one of the options is true?

Answer 3

a1 could be assigned to b1, but b1 could not be assigned to a1

Question 4

What is the name of java mechanism for passing parameters to methods?

Answer 4

call by value

Question 5

if the expression super.super.doit() appear in a method, this expression will cause a

Answer 5

Syntax error (“cause super is a key word”)

Question 6

What is the best description for overriding method?

Answer 6

Method in a base class and derived class have the same signature and the return type

Question 7

What is the best description for overloading method?

Answer 7

Two method in a class have the same name, but different numbers of parameters

Question 8

All objects of the same class will have the ___ data members and the ___ methods

Answer 8

same, same

Question 9

Java will automatically define a constructer for a class

Answer 9

If the programmer does not define any constructers for the class

Question 10

Which two of the following statements about array are FALSE?

Answer 10

• You can get the size of the array by using its length () method
• The size of an array can be changed after it has been created

Question 11

The acronym of JVM is ?

Answer 11

Java Virtual Machine

Question 12

The five exceptions related java keyword are

Answer 12

• try
• catch
• throw
• throws
• finally

Question 13

The number of simple numerical (int and floating point) data types in java is _____

Answer 13

6

• Int
• floating point
• long
• short
• double
• byte

Question 14

The name of java data type whose maximum is 32767 is

Answer 14

short

Question 15

Suppose you have the source code for a class called SomeClass in an named file and you have a command window open on the directory containing that file. Assume the file also contains the appropriate comments. Give the simplest command that will create HTML documentation for just this class and place that in a subdirectory called mydoes in the current directory:

Answer 15

javadoc -d/ directory / SomeClass

Question 16

Suppose you are preparing an executable jar file, in which the driver class is called someClass. Then your manifest file contains the line ____

Answer 16

Main-Class: SomeClass

Question 17

In java, every class is descendant of the class named:

Answer 17

Object as a super class

Question 18

The name of the only java package that you can use without explicitly import it, or any of the classes contained in it , is _____

Answer 18

java.lang.Object

Question 19

The output of the substing System.out.println(“123456”.substring(2,4)); is

Answer 19

34

Question 20

In java a ____ method is one which doesn’t have a body and it is meant to be overridden in every derived class

Answer 20

abstract methods

Question 21

In java ____ contains headings for methods that must be defined by an implementing class

Answer 21

Interfaces

Question 22

Any java block that you want to execute whether or not an exception is thrown should be placed within a ____ block

Answer 22

try

Question 23

The value of the expression 6% 12 + 5/2 is ___

Answer 23

8

Question 24

If expr1 and expr2 are both boolean expressions, the evaluation of expr2 in (expr1 || expr2) is not preformed if ____ and this called _____

Answer 24

expr1 is true , short circuit evaluation java

Question 25

The output of the code String s = “oBaMa”;
s.toUpperCase();
System.out.println(s);

Answer 25

oBaMa - because it supposed to be like this
String c = “oBaMa”;
String d = c.toUpperCase();
System.out.println(d);

Question 26

The fact that we can describe categories of objects using classes, which combine both the attributes and the behaviours that are shared by all the objects of a given category is one of the three key OOB and is called:

Answer 26

exculpation

Question 27

In UML class diagram, the symbol indicating that a method of the class private is ___

Answer 27

• (−), on the other hand, means it is private.

- (+) before an instance variable or method means the variable or method is public.

Question 28

In the following very simple UML class diagram, draw an arrow to show that the class s inherits from class t

Answer 28

Just one arrow goes from S to T

Question 29

In java once an object of type String has been created, that object cant be changed, which we describe by saying that the java strings are

Answer 29

immutable

Question 30

IF you have written a java class and want users of your class to be able to test whether two objects of that class have the same properties, then you must override, the ___ method

Answer 30

equals

Question 31

Java has a keyword that is convenient to employ when you want to use a parameters to have the same name as the private data members. The keyword is ____

Answer 31

this

Question 32

If you are writing a Java class and you want that class to implement the Comparable interface, then the only method your class must implement to do this is the _____

Answer 32

compareTo();

Question 33

if myObj is a java object reference variable for an object of any class, you can always execute the statement System.out.println(myObj); , because this causes the ____ method to be invoked on myObj, and that method is always present

Answer 33

toString

Question 34

If you want to create an object of the wrapper class integer containing the value 8, you can do this:
integer intObject = new Integer(8); , but this is no longer necessary, because a new feature called \_\_\_\_\_  was added in java 5, and now to accomplish the sam thing as the above line, you can just use the following shortcut \_\_\_\_

Answer 34

boxing, integer intObject(8);

Question 35

Give an expression involving m and n whose value is the number of times Hello is printed by the for loop shown as for(int i = m; i > =n; i–)
System.out.println(“Hello”); assue m > n

Answer 35

m + n + i

Question 36

Show on the line below what order the values 29 20 37 18 31 22 33 will have after the third pass of the outer loop has completed, when our version of the selection sort algorithm is applied

Answer 36

18 20 22 29 31 37 33
18 20 22 29 31 37 33
18 20 22 29 31 37 33
18 20 22 29 31 37 33

Question 37

Whats wrong with this code?

public class Practice {

private int n =0;
public static void main(String[] args) {

    System.out.println("n = " + n);
}

}

Answer 37

it wont run, because we either make fields static or your methods non-static.

Question 38

Whats wrong with this code?

public class Practice {

private static int n =0;
public static void main(String[] args) {

    int n;
    System.out.println("n = " + n);
}

}

Answer 38

it wont run, because; variable n might not have been initialized

Question 39

Whats wrong with this code?

public class Practice {

int n;
public static void main(String[] args) {

        Car car = new Car();
        car.getModel();
        }
        private void getModel() {
            System.out.println("n = " + n);
        }
}

Answer 39

Nothing, works fine

Question 40

What is the value of this one?

int n = 3;
int m = 4;
int result = n * (++m);

Answer 40

15

Question 41

What is the value of this one?

    int n = 3;
    int m = 4;
    int result = n * (m++);

Answer 41

12

Question 42

What is the value of this one?

 int n = 2;
        n++;
        System.out.println("n is " + n);
        n --;
        System.out.println("n is " + n);

Answer 42

n is 3

n is 2

Question 43

As a boolean expression , what is this called? (temperature > 95) || (rainFall > 20) || (humidity >= 60)

Answer 43

short-circuit evaluation or lazy evaluation

Question 44

A _____ is simply a collection of classes that have been grouped together into a folder and the name of the folder is the name of the _____

Answer 44

package , package

Question 45

each file in a package has the following line at the start of the file:

Answer 45

package Package_Name;

Question 46

The value of your _______ tells Java where to begin its search for a package,

Answer 46

class path variable

Question 47

____ can help in dealing with name clashes; that is, they can help in handling situations in which two classes have the same name.

Answer 47

packages

Question 48

A ____ is a package file format typically used to aggregate many Java class files and associated metadata and resources (text, images, etc.) into one file for distribution

Answer 48

JAR (Java Archive)

Question 49

What does recursive method means?

Answer 49

It means a method calls itself

Question 50

_____ allows you to make changes in the method definition for the derived classes and have those changes apply to the methods written in the base class.

Answer 50

Polymorphism