Learning the Java Language

Question 1

Real-world objects contain ___ and ___.

Answer 1

state and behavior

Question 2

A software object’s state is stored in ___.

Answer 2

fields - je uložený

Question 3

A software object’s behavior is exposed through ___.

Answer 3

methods - je odhalené prostredníctvom

Question 4

Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data ___.

Answer 4

encapsulation - Skrytie interných údajov pred vonkajším svetom a prístup k nim iba prostredníctvom verejne prístupných metód sa nazýva zapuzdrenie údajov.

Question 5

A blueprint for a software object is called a ___.

Answer 5

class - Návrh softvérového objektu

Question 6

Common behavior can be defined in a ___ and inherited into a ___ using the ___ keyword.

Answer 6

superclass subclass extends - a zdediť do podtriedy pomocou kľúčového slova extends.

Question 7

A collection of methods with no implementation is called an ___.

Answer 7

interface - Súbor metód bez implementácie sa nazýva rozhranie.

Question 8

A namespace that organizes classes and interfaces by functionality is called a ___.

Answer 8

package

Question 9

The term API stands for ___?

Answer 9

Application Programming Interface - Termín API je skratka pre

Question 10

The Java programming language defines the following kinds of variables:

Answer 10

1. Instance Variables (Non-Static Fields)
2. Class Variables (Static Fields)
3. Local Variables
4. Parameters

Question 11

Instance Variables (Non-Static Fields)

Answer 11

objects store their individual states in “non-static fields”, fields declared without the static keyword. = instance variables, their values are unique to each instance of a class (to each object, in other words); the currentSpeed of one bicycle is independent from the currentSpeed of another.

Question 12

Class Variables (Static Fields)

Answer 12

field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated. A field defining the number of gears for a particular kind of bicycle could be marked as static since conceptually the same number of gears will apply to all instances. The code static int numGears = 6; would create such a static field. Additionally, the keyword final could be added to indicate that the number of gears will never change.

Question 13

Local Variables

Answer 13

Similar to how an object stores its state in fields, a method will often store its temporary state in local variables. The syntax for declaring a local variable is similar to declaring a field (for example, int count = 0;). There is no special keyword designating a variable as local; that determination comes entirely from the location in which the variable is declared — which is between the opening and closing braces of a method. As such, local variables are only visible to the methods in which they are declared; they are not accessible from the rest of the class.

Question 14

Parameters

Answer 14

public static void main(String[] args) args variable = the parameter to this method. parameters are always classified as “variables” not “fields”.

Question 15

An expression

Answer 15

is a construct made up of variables, operators, and method invocations, which are constructed according to the syntax of the language, that evaluates to a single value.

Question 16

The Java programming language is statically-typed

Answer 16

which means that all variables must first be declared before they can be used, the variable’s type and name

Question 17

byte

Answer 17

is an 8-bit integer, (-128) - 127 (inclusive), for saving memory in large arrays

Question 18

short

Answer 18

is a 16-bit integer. -32 768 - 32 767, to save memory in large arrays

Question 19

int

Answer 19

is a 32-bit integer, 0 - 231

Question 20

long

Answer 20

64-bit integer, The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.

Question 21

float

Answer 21

32-bit floating point, use a float (instead of double) if you need to save memory in large arrays of floating point numbers, not for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead.

Question 22

double

Answer 22

64-bit; 0,00; For decimal values, this data type is generally the default choice, not for precise values, such as currency.

Question 23

boolean

Answer 23

two possible values: true and false, one bit of information

Question 24

char

Answer 24

16-bit Unicode character

Question 25

Integer literals can be expressed by these number systems

Answer 25

Decimal: Base 10, whose digits consists of the numbers 0 through 9;
Hexadecimal: Base 16, numbers 0-9 and the letters A-F;
Binary: Base 2, numbers 0 and 1;

Question 26

Examples of number 26 in Decimal, Hexadecimal, Binary

Answer 26

int decVal = 26;
int hexVal = 0x1a;
// The number 26, in binary
int binVal = 0b11010;

Question 27

example shows other ways you can use the underscore in numeric literals

Answer 27

long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 3.14_15F;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE;
long maxLong = 0x7fff_ffff_ffff_ffffL;
byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;

Question 28

invalid underscore placements in numeric literals

Answer 28

float pi1 = 3_.1415F;
float pi2 = 3._1415F;
long socialSecurityNumber1 = 999_99_9999_L;
OK (decimal literal) int x1 = 52; int x3 = 5_______2;
NOT OK int x2 = 52; int x4 = 0_x52; int x5 = 0x_52;
OK (hexadecimal literal) int x6 = 0x52;
NOT OK int x7 = 0x52;

Question 29

Array

Answer 29

is a container object that holds a fixed number of values of a single(jedneho) type. The length is established (stanovená) when the array is created. After creation, its length is fixed.

Question 30

An element in array

Answer 30

is each item in an array and each element is accessed by its numerical index, numbering begins with 0. The 9th element, for example, would therefore be accessed at index 8.

Question 31

a tak ďalej

Answer 31

and so forth,

Question 32

// declares an array of integers

Answer 32

int[] anArray;

Question 33

// allocates memory for 10 integers

Answer 33

anArray = new int[10];

Question 34

// initialize first element in an array
// and print the first element

Answer 34

anArray[0] = 100;

System.out.println(“Element at index 0: “ + anArray[0]);

Question 35

an array declaration

Answer 35

has two components: type[] and name, the size of the array is not part of its type (which is why the brackets are empty).

Question 36

declare arrays of other types

Answer 36

byte[] anArrayOfBytes;
short[] anArrayOfShorts;
long[] anArrayOfLongs;
float[] anArrayOfFloats;
double[] anArrayOfDoubles;
boolean[] anArrayOfBooleans;
char[] anArrayOfChars;
String[] anArrayOfStrings;

Question 37

// create an array of !10 integers

Answer 37

anArray = new int[10];

Question 38

// Each array element is accessed by its numerical index

Answer 38

System.out.println(“Element 1 at index 0: “ + anArray[0]);
System.out.println(“Element 2 at index 1: “ + anArray[1]);
System.out.println(“Element 3 at index 2: “ + anArray[2]);

Question 39

the shortcut syntax to create and initialize an array

Answer 39

int[] anArray = { 100, 200, 300 };

the length is determined by the number of values provided between braces and separated by commas

Question 40

a multidimensional array

Answer 40

an array whose components are themselves arrays

Question 41

String[][] names = {{"Mr. ", "Mrs. ", "Ms. "},{"Smith", "Jones"}}; 
// S.o.p. Mr. Smith; Ms. Jones;

Answer 41

// Mr. Smith
System.out.println(names[0][0] + names[1][0]);
// Ms. Jones
System.out.println(names[0][2] + names[1][1]);

Question 42

The System class has an arraycopy method to efficiently copy data from one array into another //

Answer 42

public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

Question 43

The following program, ArrayCopyDemo, declares an array of String elements. It uses the System.arraycopy method to copy a subsequence of array components into a second array:

Answer 43

class ArrayCopyDemo {
    public static void main(String[] args) {
        String[] copyFrom = { "Affogato", "Americano", "Cappuccino", "Corretto", "Cortado", "Doppio", "Espresso", "Frappucino", "Freddo", "Lungo", "Macchiato", "Marocchino", "Ristretto" };

    String[] copyTo = new String[7];
    System.arraycopy(copyFrom, 2, copyTo, 0, 7);
    for (String coffee : copyTo) {
        System.out.print(coffee + " ");           
    }
} } output: Cappuccino ,2,3,4,5,6, Freddo

Question 44

Pre tvoje pohodlie

Answer 44

For your convenience

Question 45

The term “instance variable” is another name for

Answer 45

Non-Static Fields

Question 46

The term “class variable” is another name for

Answer 46

Static Fields

Question 47

A local variable stores temporary state; it is declared inside

Answer 47

a method

Question 48

A variable declared within the opening and closing parenthesis of a method is called

Answer 48

a parameter

Question 49

What are the eight primitive data types supported by the Java programming language?

Answer 49

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

Question 50

Character strings are represented by the class

Answer 50

java.lang.String

Question 51

What is a container object that holds a fixed number of values of a single type?

Answer 51

An array

Question 52

Poďme vyriešiť obmedzenú verziu problému, kde potrebujeme nájsť súčet čísel, ktoré sú deliteľné 3.
Na tento účel môžeme použiť predchádzajúci prístup kontroly každého čísla a využiť základnú matematickú vlastnosť.

Answer 52

Let us solve the limited version of the problem where we need to find the sum of numbers that are divisible by 3.
For this, we can take the previous approach of checking each number of take advantage of a fundamental mathematical property.