Holy Java Moly

Question 1

JVM

Answer 1

abstract machine. a specification that provides runtime environment in which bytecode can be executed

Question 2

JRE

Answer 2

runtime environment which implements JVM and provides all class libraries and oter files taht JVM uses at runtime

Question 3

JDK

Answer 3

tool necessary to compile, document and package Java programs. completely includes JRE

Question 4

Synchronization

Answer 4

process which keeps all concurrent threads in execution to be in sync. avoids memory consistency errors caused due to inconisistent view of shared memory

Question 5

Thread

Answer 5

path of execution for a process. can run concurrently and is controlled by programmer compared to processes

Question 6

Wrapper Classes

Answer 6

each of java’s 8 primitive data types has a class dedicated to it. they “wrap” primitive data type into an object of that class.

Question 7

The 8 Primitive Types

Answer 7

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

Question 8

Boxing

Answer 8

constructing the object

Question 9

unboxing

Answer 9

extracting value from object.

Question 10

autoboxing

Answer 10

converting primitive type to wrapper

Question 11

OOPS

Answer 11

objects. can also pass by reference primitives

Question 12

final

Answer 12

used to apply restrictions on class, method and variable. class can’t be inherited, method can’t be overridden and variable value cant be changed

Question 13

finally

Answer 13

used to place important code, it will be executed whether exception is handled or not

Question 14

finalize

Answer 14

used to perform clean up processing just before object is garbage collected. gc throws away objects that are no longer used. override finalize to utilize

Question 15

StringBuffer

Answer 15

operations are thread-safe and synchronized. to be used when multiple threads are working on same String and StringBuilder in single threaded environment.

Question 16

StringBuilder

Answer 16

not thread-safe. performance is faster because of no overhead of synchronized

Question 17

String vs StringBuilder/Buffer

Answer 17

immutable vs mutable

Question 18

stack memory

Answer 18

used only by 1 thread of execution. can’t be accessed by other threads. follows LIFO manner to free memory. exists until end of execution of thread. only contains local primitive variables and reference variables to objects in heap space

Question 19

heap memory

Answer 19

used by all parts of the application. objects stored are globally accessible. memory management based on generation associated to each object. lives from start til end of app execution. whenever object is created, it’s always stored in heap space

Question 20

arraylist

Answer 20

not syncrhonized and fast. increases by 50% if element is inserted. does not define increment size. can only use Iterator for traversing an ArrayList

Question 21

vector

Answer 21

synchornized. slow and thread safe. doubles size of array when adding. defines the increment size. except hashtable, vectory is only other class which uses both Enumeration and Iterator

Question 22

hashmap

Answer 22

non synchronized and not thread safe. allows 1 null key and multiple null values. faster, traversed by Iterator. inherits AbstractMap class. can synchronize by calling Collections.synchronizedMap(hashMap)

Question 23

hashtable

Answer 23

synchronized. thread-safe and can be shared with many threads. doesn’t allow any null key/value. slow, internally synchronized and can’t be unsynchronized. traversed by Enumerrator and Iterator. inherits Dictionary class

Question 24

equals()

Answer 24

defined in Object class and used for checking equality of two objects defined by business logic. COMPARES VALUES THEMSELVES

Question 25

==

Answer 25

binary operator in Java used to compare primitives and objects. COMPARES REFERENCES