Building Blocks

Question 1

what is object?

Answer 1

An object is a runtime instance of a class in memory

Question 2

what are the two main elements of class?member of class?

Answer 2

methods and variables

Question 3

What is the keyword?

Answer 3

calls a word with special meaning

Question 4

meaning of public and class keywords?

Answer 4

public--  class can be used by other classes
class- is created class with name "toy class"

Question 5

what is the void?

Answer 5

it is a return type and no need to return value for that method

Question 6

what is the method signature?

Answer 6

a full declaration of method

Question 7

public int numberVisitors(int month)

Answer 7

int-return type,
numberVisitor-name of the method
(int month)- parameter

Question 8

comment types

Answer 8

//--one line,
/* * * /*-- multiple line comment
/**  * * .  /*- javadoc comment

Question 9

does it proper class

Answer 9

class toy { 
String str;
}

Question 10

does it proper class?

Answer 10

public class phone{
}
class smartPhone{
String name;
}

Question 11

What is the main() method?

Answer 11

A main() method is the gateway between the startup of a Java process, which is managed by the Java Virtual Machine (JVM), and the beginning of the programmer’s code.

Question 12

java file extension

Answer 12

.java

Question 13

bytecode extension?

Answer 13

.class

Question 14

the correct main method parameters?

Answer 14

String[] args, String args[] or String… args;

Question 15

how could be create an objects?

Answer 15

by using constructors—- Random random=new Random();

Question 16

Random random=new Random();

Answer 16

Random random----declare the variable
new Random()---- create an aobject on the heap memory

Question 17

two main specs for constructors?

Answer 17

the name of constructor is same as class name,
no any return type in constructors,

Question 18

what is the code block?

Answer 18

between bracies–{ }

Question 19

what is the code block?

Answer 19

between bracy–{ }

Question 20

instance initiliazier?

Answer 20

when count it, just in the methods,

Question 21

what are the variables?

Answer 21

primetives and reference type

Question 22

what are pirimitives?

Answer 22

boolean, char, short, long, int, long, float, double store in the stack memeory and store values always

Question 23

what is the reference types?

Answer 23

it is a handle to refer an object on the heap.

Question 24

difference between primetives and reference types

Answer 24

holds a value, store in stack, not call any methods, never be null, when using equaility copied,
handle to refer the object, in heap, can be null, call any methods, when equality not copied object

Question 25

what is declearing?

Answer 25

String str, int numHome;

Question 26

what is initiliazing?

Answer 26

String str="maer";

Question 27

does it work

Answer 27

int num, String value;

Question 28

important identifier names rules in Java?

Answer 28

must begin with a letter or the symbol $ or _. Subsequent characters may also be numbers. cannot use the same name as a Java reserved word.

Question 29

bad example for identifier names?

Answer 29

3DPointClass // identifiers cannot begin with a number hollywood@vine // @ is not a letter, digit, $ or _ *$coffee // * is not a letter, digit, $ or _ public // public is a reserved word

Question 30

local variables

Answer 30

define in method initiliazed before use not have a default value

Question 31

instance variables

Answer 31

``` Instance variables are also called fields. variable is a class variable if it has the static keyword in its declaration ```

Question 32

instance and class variables

Answer 32

Instance and class variables do not require you to initialize them. As soon as you declare these variables, they are given a default value.

Question 33

order by package and import and class

Answer 33

``` package structure; // package must be first non-comment import java.util.*; // import must come after package public class Meerkat { // then comes the class double weight; // fields and methods can go in either order public double getWeight() { return weight; } double height; // another field – they don't need to be together ```

Question 34

class structure in the order

Answer 34

multiple classes can be defined in the same file, but only one of them is allowed to be public. The public class matches the name of the file.

Question 35

Benefits of Java

Answer 35

Java is an object-oriented language, which means all code is defined in classes and most of those classes can be instantiated into objects.

Question 36

Benefits of Java

Answer 36

Encapsulation Java supports access modifiers to protect data from unintended access and modification.