90041 Java

Front 1

A program that connects the byte-code of the classes needed to run a Java program ?

Back 1

Class Loader

Front 2

The arrangement of wordsand punctuations that are legal in alanguage, the grammar rules of alanguage

Back 2

Syntax

Front 3

The meaning of thingswritten while following the syntax rulesof a language

Back 3

Semantics

Front 4

Bits in a byte

Back 4

8

Front 5

Bytes in a boolean

Back 5

1

Front 6

Bytes in a char

Back 6

2

Front 7

Bytes in a byte

Back 7

1

Front 8

Bytes in a short

Back 8

2

Front 9

Bytes in an int

Back 9

4

Front 10

Bytes in a long

Back 10

8

Front 11

Bytes in a float

Back 11

4

Front 12

Bytes in a double

Back 12

8

Front 13

What is the print f format + "%.

Back 13

x = Number to right justify

y = Number of digits to display after decimal place

c = The type output representation

Front 14

Format specifiers :

d

f

e

g

s

c

Back 14

d = Decimal integer

f = Fixed-point floating point

e = Enotation floating point

g = general floating point

s = string

c = character

Front 15

How to create a Scanner object for getting input from console ?

Back 15

new java.util.Scanner(System.in)

Front 16

the next... methods of a Scanner object ?

Back 16

nextLine

nextInt

nextDouble

..

and so on

Front 17

Does the nextLine method of a Scanner object remove and discard the delimiter?

Back 17

Yes

Front 18

How to change the delimiter of a Scanner class ?

Back 18

Scanner.useDelimiter("##")

Front 19

How to specifically avoid short circuiting using the AND or OR operators

Back 19

Use & instead of &&

Use | instead of ||

Front 20

What is the syntax of a switch statement

Back 20

Switch(a) :

{

case 1 :

statement;

break;

case 2:

statement;

break;

default:

break;

}

Front 21

What are the two multi-way branching loops

Back 21

The nested "if else-if" and "switch"

Front 22

What are the three types of loops in java ?

Back 22

While

Check condition then execute

Do-While

Execute then check condition

For

Initialize, Compare, Execute, then execute statement

Front 23

What do the break and continue commands do ?

Back 23

break: Exits the innermost for, while or do while loop.

Continue: Skip to the next iteration of the innermost loop, skipping and code below it. In the case of a for loop, control goes to the update part.

Front 24

How would you label a loop ?

Back 24

label:

do{

}while(a >1);

Front 25

Write a do while loop

Back 25

do{

...

...

}while(condition);

Don't forget the semicolon!

Front 26

In a for loop how would you have multiple initialization ?

Back 26

for(int i = 0, int j = 1; i<0 && j >2; i++){

}

Use a comma

Front 27

How to use the assert command

Back 27

assert Boolean_Expression;

Front 28

What kind of scope does java have?

Back 28

Block scope

Front 29

When must the this parameter be used ?

Back 29

When a local variable has the same name as an instance variable in the calling object.

Front 30

What methods does java expect all classes to have ? And write their method definitions.

Back 30

String toString()

boolean equals(classname object)

Front 31

What does information hiding mean ?

Back 31

Information hiding is the practice of separating howto use a class from the details of its implementation using private, public,protected modifiers.

Front 32

What does Encapsulation mean ?

Back 32

Encapsulation means that the data and methods ofa class are combined into a single unit (i.e., a classobject), which hides the implementation details

Front 33

What is Overloading ?

Back 33

Overloading is when two or more methods inthe same class have the same method name.

In general no two methods can have the same combination of method name and parameter lists.

Front 34

Does Java permit methods with thesame name and different return typesin the same class ?

Back 34

No

Front 35

What does the StringTokenizer class do ?

Back 35

The StringTokenizer class is used torecover the words or tokens in a multi-wordString.

– You can use whitespace characters to separateeach token, or you can specify the charactersyou wish to use as separators

– In order to use the StringTokenizer class, besure to include the following at the start of the file:import java.util.StringTokenizer;

StringTokenizer is LEGACY. User String.split() instead.

Front 36

Explain the following methods of String Tokenizer :

hasMoreTokens()

nextToken()

nextToken(String delimiters)

countTokens()

Back 36

hasMoreTokens() : Tests if there are more tokens available from this tokenizer's string.

nextToken() : Returns the next token from this string tokenizer.

nextToken(String delim)Returns the next token in this string tokenizer's string.

countTokens() :

Calculates the number of times that this tokenizer's nextToken method can be called before it generates an exception.

Front 37

Can a class static method call non static methods within the same class ?

Back 37

No

Front 38

Does a java static method have a this variable ?

Back 38

No!

Front 39

What methods and variable can a static method access ?

Back 39

Other static variables and other static methods.

Front 40

What limitations are there on static variables ?

Back 40

A static variable should always be defined private, unless it is also a defined constant

The value of a static defined constant cannot be altered, therefore it is safe to make it public

In addition to static, the declaration for a static defined constant must include the modifier final, which indicates that its value cannot be changed

Front 41

What are some methods in the java math class ?

Back 41

// Return smallest whole number greater than or equal to argument

- Ceil(a)

// opposite

- floor(a)

-sqrt()

- Min( a, b)

- Pow(base, exponent)

- abs()

// To nearest whole number
- round()

Front 42

What are wrapper classes ?

Back 42

Wrapper classes are classes which emulate and extend the functionality of the primitive types :

boolean,int,short,byte,char,long,float,double,

Front 43

What is Boxing ?

Back 43

Boxing: the process of going from a value of a primitive type to an object of its wrapper class–

To convert a primitive value to an "equivalent" class type value, create an object of the corresponding wrapper class using the primitive value as an argument

The new object will contain an instance variable that stores a copy of the primitive value

Front 44

Why is boxing important ?

Back 44

Because primitive types are not classes.. Therefore they cannot be used with some of the java standard library (importantly Generics).

For Example, java.util.Vector<>

Front 45

What is Boxing and how to achieve it ?

Back 45

Unboxing: the process of going from an object of a wrapper class to the corresponding value of a primitive type

Front 46

What is unboxing and how is it achieved ?

Back 46

Unboxing: the process of going from an object of a wrapper class to the corresponding value of a primitive type

Unboxing is achieved by a call to intValue,charValue,doubleValue, etc etc

Front 47

What is automatic boxing and unboxing ?

Back 47

Instead of creating a wrapper class object using the new operation (as shown before), it can be done as an automatic type cast:Integer integerObject = 42;

Instead of having to invoke the appropriate method (such as intValue, doubleValue, charValue, etc.) in order to convert from an object of a wrapper class to a value of its associated primitive type, the primitive value can be recovered automaticallyint i = integerObject;

Front 48

What are some use full constants in the wrapper classes ?

Back 48

For example, Integer.MAX_VALUE,Integer.MIN_VALUE, Double.MAX_VALUE, Double.MIN_VALUE, etc.

Front 49

How would you parse a string as a type using a wrapper class ?

Back 49

Wrapper classes have static methods that convert a correctly formed string representation of a number to the number of a given type

The methods Integer.parseInt,

Long.parseLong,

Float.parseFloat,

Double.parseDouble

convert a correctly formed string into the PRIMITIVE TYPE

Front 50

How would you represent a primitive type as a string ?

Back 50

1 - Either box the primitive type and then call toString() on the object.

2 - Use the static method which will take a primitive type and convert it into a string. For example : Integer.toString(2) will give a string "2"

Front 51

What usefull methods does the Character wrapper class have ?

Back 51

toUperCase

toLowerCase

isUpperCase

isLowerCase

isWhiteSpace

IsLetter

isDigit

isLetterOrDigit

Front 52

Are java parameters in methods call by value or call by reference ?

Back 52

CALL BY VALUE

However variables pointing at classes behave as if they are call by reference because this variables are behind the scenes actual references.

Front 53

What is the "null" value in java

Back 53

The null value denotes a lack of a class. For example one can do String s= null. Which basically means that s is currently not holding any object.

Front 54

What does the == operator do in this statement;

object a == object b ?

Back 54

The == operator only checks that two class type variableshave the same memory address

Front 55

What is an immutable object

Back 55

A class that contains no methods (otherthan constructors) that change any of thedata in an object of the class is called animmutable class

Front 56

Explain deep copy versus shallow copy

Back 56

A deep copy of an object is a copy that, withone exception, has no references incommon with the original– Exception: References to immutable objects areallowed to be shared.

Any copy that is not a deep copy is called ashallow copy– This type of copy can cause dangerous privacyleaks in a program

Front 57

Give 3 ways to initialize and declare an array

Back 57

int[] myIntArray = new int[3];

int[] myIntArray = {1,2,3};

int[] myIntArray = new int[]{1,2,3};

Front 58

How do you determine the length of an array ?

Back 58

if int[] a = new int[]{1,2,3,4};

then the length is a.length

Front 59

What are arrays in java ? Primitive types or references types ?

Back 59

Reference Types

Front 60

What does the statement below do :

String[] s = new String[20];

Back 60

Creates a new array of strings of length 20. each of the elements in the array will be a null variable, NOT an empty string object.

Front 61

What type of array is the args parameter of the main method

Back 61

the main method looks like :

public static void main(String[] args){}

So a String array.

Front 62

Where can the for-each loop apply ?

Back 62

The standard Java libraries include a number ofcollection classes– Classes whose objects store a collection of values. Collection is an interface.

This kind of loop can cycle through each element ina collection even though the elements are notindexed

Front 63

What is the syntax for a for each loop

Back 63

for( Type i : Collection){}

Front 64

Give a simple example of defining an enumerated type ?

And then access the enum

Back 64

public enum etype{Value1,Value2};

etype a = etype.Value1;

Front 65

Given the following :

enum Workday{Monday,Tuesday,Wednesday};

Workday z = Workday.Monday;

System.out.println(Workday.Monday);

System.out.println(z);

Back 65

The first line would print out "Monday"

The second line would also print out "Monday"

Front 66

What does the values() method of an enum do ?

Back 66

It returns an array whose elements are the values of theenumerated type given in the order in which the elementsare listed in the definition of the enumerated type

For example the following :

enum[] a = enum.values();

Front 67

How can enums be used in a switch statement and what is the syntax ?

What is an important caveat ?

Back 67

given enum color{RED,BLUE,GREEM};

color Z = color.RED;

switch (z):

{

case RED:

break;

default:

break;

}

Front 68

What is a co variant return type ?

Back 68

Ordinarily, the type returned may not bechanged when overriding a method

However, if it is a class type, then thereturned type may be changed to that of anydescendent class of the returned type

This is known as a covariant return type –

Covariant return types are new in Java 5.0; theyare not allowed in earlier versions of Java

Front 69

Can the Access Permission of anOverridden Method be changed ?

Explain how ?

Back 69

The access permission of an overriddenmethod can be changed from private in thebase class to public (or some other morepermissive access) in the derived class

However, the access permission of anoverridden method can not be changed frompublic in the base class to a more restrictedaccess permission in the derived class

Front 70

Can a child both overload and override an inherited method at the the same time ?

Back 70

Yes. Both the overriden method and overloaded method will exist in the child.

If only the method is overloaded then the inherited default method will also be in the child !

Front 71

How can you prevent a class from being extended ?

Back 71

Put the final modifier in the class header.

Front 72

How can you prevent a method from being extended ?

Back 72

Put the final modifier in the method header.

Front 73

How can you prevent a method or variable from being inherited ?

Back 73

Making that variable of method private.

Front 74

How would you make a a method heritable but not capable of being overridden ?

Back 74

Placing public or protected in the header along with final.

Front 75

How can a class prevent its children from inherting its methods or variables

Back 75

By using the private keyword

Front 76

How can a class prevent the public from accessing its objects and variables but still allow children to inherit ?

Back 76

Use the protected modifier.

Front 77

What are some rules of using the super constructor ?

Back 77

A call to super must always be the firstaction taken in a constructor definition

An instance variable cannot be used as anargument to super

If no super constructor is specifically invoked then the default constructor will be invoked.

Front 78

During construction of a child - calling this before calling the super constructor is legal as long as the call to the this constructor first calls a super as its first action. Is this legal ? Give an example ?

Back 78

Yes legal. Look at parent.java and child.java

Front 79

What unchecked exceptions might the next...() methods of the scanner class throw and if import statements are required to catch them write them down.

Back 79

java.util.InputMismatchException;

java.util.NoSuchElementException;