Java Se 8 Programmer I 1Z0-808

Front 1

Valid Comments in Java

Back 1

Single Line (//)

multi-line (/* */)

Javadoc comment (/** */)

Front 2

Java code is executed with this statement

Back 2

main method:

public static void main(String[]args){

}

Front 3

Redundant Imports

Back 3

java.lang doesn't need to be imported

Wild card statements

Front 4

Constructors

Back 4

Creates Java objects. Has the same name as java class and no return type.

Example: public class Ending{

public Ending { }

}

Front 5

byte type

Back 5

8 bit. Numbers -128 to 127.

Front 6

Octal, Hexadecimal and Binary

Back 6

■Octal (digits 0–7), which uses the number 0 as a prefix—for example, 017 BASE 10

■ Hexadecimal (digits 0–9 and letters A–F), which uses the number 0 followed by x or Xas a prefix—for example, 0xFF

■ Binary (digits 0–1), which uses the number 0 followed by b or B as a prefix—for example,0b10

Front 7

Rules for Literals and Underscores

Back 7

You can addunderscores anywhere except at the beginning of a literal, the end of a literal, right before adecimal point, or right after a decimal point.

Front 8

Declaring multiple variables

Back 8

Declare as many variables of same type in one line, as well as initialize them. eg.

boolean b1, b2; // Legal

String s1 = "1", s2; //Legal

double d1, double d2; // Not legal

int i1; int i2; // Legal

int i3; i4; // i3 legal i4 is not

Front 9

Identifiers (Name of variable)

Back 9

■ The name must begin with a letter or the symbol $ or _.

■ Subsequent characters may also be numbers.

■ Cannot use Java keywords eg. public, class, int

Front 10

Order of Initialization

Back 10

■ Fields and instance initializer blocks are run in the order in which they appear inthe file.

■ The constructor runs after all fields and instance initializer blocks have run.

Front 11

Local Variable Scope and rules

Back 11

■Must be initialized otherwise doesn't compile.

■ Scope ends at the end of block

Front 12

Default values for:

boolean,

byte, short, int, long

float, double

char

All object references (everything else)

Back 12

boolean: false

byte, short, int, long: 0 (in the type’s bit-length) float, double: 0.0 (in the type’s bit-length)

char: '\u0000' (NUL)

All object references (everything else): null

Front 13

Ordering Elements in a Class

Back 13

Package declaration EG. package abc;

Not required. First line in the file

Import statements EG. import java.util.*; Not required.Immediately after the package

Class declaration EG. public class C

Required. Immediately after the import

Field declarations EG. int value;

Not required. Anywhere inside a class

Method declarations eg. void method(){}

Not required. Anywhere inside a class

Front 14

Garbage collection for Object

Back 14

■ The object no longer has any references pointing to it.

■ All references to the object have gone out of scope.

Front 15

finalize()

Back 15

finalize() is only run when the object is eligible for garbage collection.

Front 16

Numeric Promotion Rules

Back 16

1. If two values have different data types, Java will automatically promote one of the valuesto the larger of the two data types.

2. If one of the values is integral and the other is floating-point, Java will automaticallypromote the integral value to the floating-point value’s data type.

3. Smaller data types, namely byte, short, and char, are first promoted to int any timethey’re used with a Java binary arithmetic operator, even if neither of the operands isint.

4. After all promotion has occurred and the operands have the same data type, the resultingvalue will have the same data type as its promoted operands.

Front 17

Increment and Decrement Operators

Back 17

pre-increment operator, the operator is applied first and the value returnis the new value of the expression. post-increment operator , then the originalvalue of the expression is returned, with operator applied after the value is returned.

eg.

int counter = 0;System.out.println(counter); // Outputs 0System.out.println(++counter); // Outputs 1System.out.println(counter); // Outputs 1System.out.println(counter--); // Outputs 1System.out.println(counter); // Outputs 0

int x = 3;

int y = ++x * 5 / x-- + --x;

y= 4 * 5 / 4 + 2;

x = 2

y = 7.

Front 18

Casting Primitive Values

Back 18

Required when larger numerical datatype to smaller numerical data type, or

converting from a floating-point number to anintegral value.

eg.

int x = (int)1.0;

short y = (short)1921222; // Stored as 20678

int z = (int)9l;

long t = 192301398193810323L;

Front 19

OR, AND, EXCLUSIVE

Back 19

And symbol &

Or Symbol |

exclusive ^

Front 20

Equality Operator

Back 20

1.Comparing two numeric primitive types. For example,5 == 5.00 returns true since the left side is promoted to a double.

2. Comparing two boolean values.

3. Comparing two objects, including null and String values

-Two references are equal if and only if they point to the sameobject, or both point to null.

Front 21

Ternary Operator

Back 21

booleanExpression ? expression1 : expression2

Front 22

Switch statement contruction

Back 22

switch(variableToTest) {

case constantExpression1:

// Branch for case1;

case constantExpression2:

// Branch for case2;

...

default:// Branch for default

}

Int and Integer, byte and Btye, short and Short, char and Character, String and enum values

Front 23

Basic for statement

Back 23

for(initialization; booleanExpression; update) {

// Body

}

1) Initialization statement executes

2)If booleanExpression is true continue, else exit loop

3)Body executes

4)Execute updateStatements

5)Return to Step 2

Front 24

Basic for-each statement

Back 24

for(datatype instance : collection)

{

// Body

}

Front 25

Advanced Flow control - Nested flow control

Back 25

int[][] myComplexArray = {{5,2,1,3},{3,9,8,9},{5,7,12,7}};

for(int[] mySimpleArray : myComplexArray) { for(int i=0; i

System.out.println(mySimpleArray[i]+"\t");

}

System.out.println();

}

Front 26

Break statement

Back 26

optionalLabel: while(booleanExpression) {

// Body

// Somewhere in loop

break optionalLabel;

}

Front 27

Immutability

Back 27

String object is created, it is not allowed to change.

String s1 = "1";

String s2 = s1.concat("2");

s2.concat("3");

System.out.println(s2); // = 12

Front 28

String Pool

Back 28

String name = "Fluffy";String name = new String("Fluffy");

The second says “No, JVM. I reallydon’t want you to use the string pool. Please create a new object for me even though it isless efficient.”

Front 29

substring()

Back 29

String string = "animals";System.out.println(string.substring(3)); // malsSystem.out.println(string.substring(string.indexOf('m'))); // malsSystem.out.println(string.substring(3, 4)); // mSystem.out.println(string.substring(3, 7)); // mals

Front 30

equals() and equalsIgnoreCase()

Back 30

equals() method checks whether two String objects contain exactly the same charactersin the same order.

equalsIgnoreCase() same as equals() but ignores case.

Front 31

replace()

Back 31

String replace(char oldChar, char newChar)String replace(CharSequence oldChar, CharSequence newChar)

Front 32

trim()

Back 32

removes whitespace from the beginning and endof a String.

Front 33

StringBuilder class

Back 33

mutable

StringBuilder sb1 = new StringBuilder();StringBuilder sb2 = new StringBuilder("animal");StringBuilder sb3 = new StringBuilder(10);

// tells java we have a 10 capacity string

Front 34

indexOf()

Back 34

String string = "animals";System.out.println(string.indexOf('a')); // 0System.out.println(string.indexOf("al")); // 4System.out.println(string.indexOf('a', 4)); // 4System.out.println(string.indexOf("al", 5)); // -1

Front 35

delete() and deleteCharAt()

Back 35

StringBuilder delete(int start, int end)StringBuilder deleteCharAt(int index)

Front 36

Equality in Strings and Objects. Difference between == and equals

Back 36

"==" checks if two references point ot the same object.

"equals" checks if what's inside the string is the same. EG.

String x = "Hello World";

String z = " Hello World".trim();System.out.println(x.equals(z)); // true but "x==z" is false

Front 37

Multiple “Arrays” in Declarations

Back 37

int[] ids, types; // Two int [] arrays

int ids[], types; //one ids array and one int variable

Front 38

Sorting Arrays

Back 38

Needs import statement:

import java.util.*; //or
import java.util.Arrays;

//Used like Arrays.sort(Array here);

Sorts ints correctly

Sorts Strings 1-9, UPPERCASE A-Z, lowercase a-z

Front 39

Searching Arrays

Back 39

Needs import statement:

import java.util.*; //or

import java.util.Arrays;

/* Used like

Arrays.binarySearch( Array here, index)); */

Rules:

Target element found in sortedarray--->

Index of match

Target element not found insorted array ------------->Negative value showing one smaller than thenegative of index, where a match needs to beinserted to preserve sorted order

Front 40

Multi-Dimensional Array

Back 40

int[][] vars1; // 2D array

int vars2 [][]; // 2D array

int[] vars3[]; // 2D array

int[] vars4 [], space [][]; // a 2D AND a 3D array

Front 41

ArrayList

Back 41

Have to import:

import java.util.* // import whole package OR

import java.util.ArrayList;

ArrayList list1 = new ArrayList();

ArrayList list2 = new ArrayList(10);

ArrayList list3 = new ArrayList(list2);

ArrayList list4 = new ArrayList();

ArrayList list5 = new ArrayList<>();

List list6 = new ArrayList<>();

Front 42

add () method

Back 42

For ArrayList,

boolean add (E element)

void add (int index, E element)

Front 43

remove()

Back 43

boolean remove (Object object)

E remove (int index)

Front 44

Converting between Array and ArrayList

Back 44

toArray() method used to turn ArrayList to Array.

Arrays.asList(Array) method used to turn Array to ArrayList.

Front 45

Sorting ArrayList or List

Back 45

Method:

Collections.sort(ArrayList arraylist);

Front 46

First thing to do to use Dates and Times on

JAVA 8

Back 46

import time classes

import java.time.*;

Front 47

Classes of date and time

Back 47

LocalDate

LocalTime

LocalDateTime

Front 48

LocalDate of Method

Back 48

public static LocalDate of(int year, int month, int dayofMonth)

public static LocalDate of(int year, MONTH month, int dayofMonth)

Front 49

Methods in LocalDate, LocalTime, and LocalDateTime

Back 49

Front 50

Working with Periods

Back 50

Period annually = Period.ofYears(1); // every 1 year

Period quarterly = Period.ofMonths(3); // every 3 monthsWorking with Dates and Times 147

Period everyThreeWeeks = Period.ofWeeks(3); // every 3 weeks

Period everyOtherDay = Period.ofDays(2); // every 2 days

Period everyYearAndAWeek = Period.of(1, 0, 7); // every year and 7 days

Front 51

Formatting Dates and Times

Back 51

/* Use DataTimeFormatter class - inside the java.time.format package */

Front 52

Formatting Dates and Times - Simple example/ syntax

Back 52

Front 53

PARSING DATES AND TIMES TO STRING

Back 53

DateTimeFormatter.ofPattern("MM dd yyyy");

LocalDate date = LocalDate.parse("01 02 2015", f);

LocalTime time = LocalTime.parse("11:22");

Syst.println(date); // 2015-01-02

Syst.println(time); // 11:22

Front 54

Method Signature & declaration

Back 54

Front 55

ACCESS MODIFIERS

Back 55

*public

*private

*protected

*Default (Package private) access

Front 56

METHOD OPTIONAL SPECIFIER

Back 56

*static

*abstract

*final

*synchronized

Front 57

METHOD RETURN TYPE

Back 57

ALLOWED:
int integer(){

return 9;

}

NOT ALLOWED:

int long(){

return 9L;

}

Front 58

METHOD NAMES

Back 58

SAME AS VARIABLE NAMES.

*ONLY LETTERS, NUMBERS, $ sign, or UNDERSCORE _

*CANNOT START WITH NUMBER

Front 59

WORKING with Varargs

Back 59

-Like arrays

-Must be the last element in parameter list

-Can only have one

EXAMPLE:

public static void walk(int x, int... nums){

sys.print(nums.length);

}

walk(1); // 0

walk(1, 2) // 1

walk(1,3,3)// 2

etc..

Front 60

Applying Access Modifiers to methods

Back 60

Private: Accessible within the same class

default: private and other classes in the same package

protected: default access and child classes

public: protected and classes in the other packages

Front 61

Gotcha's of protected modifier:

Back 61

See screenshot.