Code Snippets Java 8

List of Java 8 topics and their code snippets!

Package definition and imports

Import Class

import java.util.Scanner;

Import Package

import java.util.*;

Comments

Single line comment

// Single line comment or End-of-line comment

Multi-line comment

/* Multi-line comment
or Inline comment 
or Block comment */

Documentation comment

/**
* 
* Documentation comment used for explaining code
* Spans multiple lines
*
**/

Printing to Console

System.out.println("Hello World");

Data Types

Primitive or Value types

byte myByte = 6;
short myShort = 7;
int myInt = 5234;
long myLong = 232245;
float myFloat = 5.99F;
double myDouble = 2.55;
char myChar = 'S';
boolean myBool = true;

Non-primitive or Reference or Object types

Byte myByte = 6;
Short myShort = 7;
Integer myInt = 5234;
Long myLong = 2322L;
Float myFloat = 5.99F;
Double myDouble = 2.55;
Character myChar = 'S';
Boolean myBool = true;
String myString = "Hello World!";

Constants and Variables

final String name = "Hithesh";
int age = 75;
static String profession = "Android Developer";

Operators

Arithmetic Operators

6 + 2
6 - 2
6 * 2
6 / 2
6 % 2
++6
--6

Assignment Operators

final int a = 6;
a = 5;
a += 3;
a -= 1;
a *= 6;
a /= 2;
a %= 3;
a &= 2;
a |= 3;
a ^= 5;
a >>= 3;
a <<= 5;

Comparison Operators

final int a = 6, b = 2;
a == b
a != b
a > b
a < b
a >= b
a <= b

Logical Operators

final int a = 6, b = 2;
a < 5 && b > 4
a < 5 || b > 4 
!(a < 5 && b > 4)

Conditionals

If, else and else if statements

final int a = 6, b = 2;
if (a > 3 && b > 1) {
    System.out.println("Allowed");
} else if (a == 3 || b > 1) {
    System.out.println("Allowed");
} else {
    System.out.println("Not Allowed");
}

Ternary Operator

final String result = (a > 3 && b > 1) ? "Allowed" : "Not Allowed";

switch statements

switch (a) {
    case 3:
        System.out.println("Not Allowed");
        break;
    case 4:
        System.out.println("Allowed");
        break;
    default:
        System.out.println("Not Allowed");
        break;
}

Loops

For Loop

final int[] arr = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
final int[] arrCharAsciiNums = new int[]{'a', 'b', 'c', 'd', 'e', 'f'};  // this also gives ASCII nums of the chars
final char[] arrChars = new char[]{'a', 'b', 'c', 'd', 'e', 'f'};
final List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
final Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Hithesh");
map.put(2, "Iitesh");
map.put(3, "Jitesh");

for (int i = 0; i < arr.length; i++) {
    System.out.print(arr[i] + " "); // 1 2 3 4 5 6 7 8 9 10
}

for (int i = 0; i <= arr.length - 1; i++) {
    System.out.print(arr[i] + " "); // 1 2 3 4 5 6 7 8 9 10
}

for (int i = arr.length - 1; i >= 0; i--) {
    System.out.print(arr[i] + " "); // 10 9 8 7 6 5 4 3 2 1
}

for (int i = 0; i <= arr.length - 1; i += 2) {
    System.out.print(arr[i] + " "); // 1 3 5 7 9
}

for (int i = arr.length - 1; i >= 0; i -= 2) {
    System.out.print(arr[i] + " "); // 10 8 6 4 2
}

for (int num : arr) {
    System.out.print(num + " "); // 1 2 3 4 5 6 7 8 9 10
}

for (Map.Entry<Integer, String> num : map.entrySet()) {
    System.out.print(num + " "); // 1=Hithesh 2=Iitesh 3=Jitesh
}

for (Map.Entry<Integer, String> num : map.entrySet()) {
    System.out.print(num.getKey() + " "); // 1 2 3
}

for (Map.Entry<Integer, String> num : map.entrySet()) {
    System.out.print(num.getValue() + " "); // Hithesh Iitesh Jitesh
}

For-Each Loop

for (int num : arr) {
    System.out.print(num + " ");	// 1 2 3 4 5 6 7 8 9 10 
}

While Loop

int i = 0;
while (i < 5) {
    System.out.println(i);
    i++;
}

Do-While Loop

int i = 1;
do {
    System.out.print(i + " ");	// 1 2 3 4 5 6 7 8 9 10 
    i++;
} while (i <= 10);

Break

for (int i = 0; i < arr.length; i++) {
    if (i == 6) break;
    System.out.print(i + " ");	// 0 1 2 3 4 5 
}

Continue

for (int i = 0; i < arr.length; i++) {
    if (i == 2) continue;
    if (i == 6) continue;
    System.out.print(i + " ");	// 0 1 3 4 5 7 8 9
}

Label

Work1:
for (int i = 0; i < 5; i++) {
    Work2:
    for (int j = 0; j < 6; j++) {
        if (i == 3) continue Work1;
        System.out.print("i=" + i + ", j=" + j + " | ");	// i=0, j=0 | i=0, j=1 | i=0, j=2 | i=0, j=3 | i=0, j=4 | i=0, j=5 | i=1, j=0 | i=1, j=1 | i=1, j=2 | i=1, j=3 | i=1, j=4 | i=1, j=5 | i=2, j=0 | i=2, j=1 | i=2, j=2 | i=2, j=3 | i=2, j=4 | i=2, j=5 | i=4, j=0 | i=4, j=1 | i=4, j=2 | i=4, j=3 | i=4, j=4 | i=4, j=5 |
    }
}

Compute Loop time

final long startTime = System.nanoTime();

int y = 0;
while (y < 100) {
    y++;
}

final long endTime = System.nanoTime();
final long timeTaken = endTime - startTime;
System.out.println("Time taken for this loop: " + timeTaken / 1.0E9 + " seconds"); // 48.387187825 seconds
System.out.printf("Time to compute: %5.1f seconds.%n", timeTaken / 1.0e9); // 48.4 seconds.

For loop as While loop

for (long x = 0; ; ) {	// for loop that acts like while loop
    System.out.println("Iteration: " + x);
    if (x == 100000000000L) break;
    x++;
}

Collections

ArrayList

// Create
final ArrayList<String> myAnimeList = new ArrayList<String>();
myAnimeList.add("Code Geass");
myAnimeList.add("Death Note");
myAnimeList.add("Eccentric Family");
myAnimeList.add("Steins;Gate");
myAnimeList.add("Attack On Titan");
myAnimeList.add("Made In Abyss");
myAnimeList.add("Dragon Ball Z");
myAnimeList.add("Fate/Zero");
myAnimeList.add("Ghost In The Shell");
myAnimeList.add("One Punch Man");
myAnimeList.add("Mobile Suit Gundam 00");
myAnimeList.add("Monster");
myAnimeList.add("School Rumble");

// Print
System.out.println(myAnimeList);

// Read
myAnimeList.get(0);
myAnimeList.size();

// Update
myAnimeList.set(0, "Code Geass R2");

// Iterate
for (int i = 0; i < myAnimeList.size(); i++) {
    System.out.println(myAnimeList.get(i));
}
for (String anime : myAnimeList) {
    System.out.println(anime);
}

// Sort
Collections.sort(myAnimeList);

// Delete specific element
myAnimeList.remove(6);

// Delete All
myAnimeList.clear();

HashMap

// Create, Update
final HashMap<Integer, String> myAnimeList = new HashMap<Integer, String>();
myAnimeList.put(1, "Code Geass");
myAnimeList.put(2, "Death Note");
myAnimeList.put(3, "Eccentric Family");
myAnimeList.put(4, "Steins;Gate");
myAnimeList.put(5, "Attack On Titan");

// Print
System.out.println(myAnimeList);

// Read
myAnimeList.get(1); // get by key
myAnimeList.size();

// Iterate
for (Map.Entry<Integer, String> animeSet : myAnimeList.entrySet()) {
    System.out.println(animeSet.getKey() + " " + animeSet.getValue());
}

// Iterate For-each
myAnimeList.forEach((key, value) -> System.out.println(key + " = " + value));

// Iterate with Iterator
final Iterator<Map.Entry<Integer, String>> it = myAnimeList.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry<Integer, String> set = (Map.Entry<Integer, String>) it.next();
    System.out.println(set.getKey() + " = " + set.getValue());
}

// Iterate over Keys
for (Integer animeRank : myAnimeList.keySet()) {
    System.out.println(animeRank);
}

// Iterate over Values
for (String anime : myAnimeList.values()) {
    System.out.println(anime);
}

// Delete specific element
myAnimeList.remove(5);  // Remove by key

// Delete All
myAnimeList.clear();

Queue
- Queue = FIFO data structure. First-In, First-Out. A collection designed to holding elements prior to processing. Linear Data Structure
- Enqueue = offer() - add an element to the end of the queue
- Dequeue = poll() - remove an element from the start of the queue
- Used in Keyboard Buffer - letters should appear on the screen in the order they are pressed
- Used in Printer Queue - print jobs should be completed in order
- Used in LinkedLists, Priority Queues, Breadth-First Search

final Queue<String> queue = new LinkedList<String>();

// Create or Add
queue.offer("Hithesh");
queue.offer("Iithesh");
queue.offer("Jithesh");
queue.offer("Kithesh");

queue.poll(); // deletes the topmost element from queue

final String latestPerson = queue.peek();   // read but dont write or modify

System.out.println(queue.size());
System.out.println(queue.isEmpty());
System.out.println(queue.contains("Hithesh"));

Bitwise Operations

What is binary:
what is decimal 3 in binary? 32 bit int java. - 000...011
what is decimal 6 in binary
Bitwise operations can be performed on any of the integral types - integral types (char, short, int, etc)
How is a decimal value like a number represented in binary in Java: Java Integer is 32 bit. So the value of say 4 in binary is 00000...0100.
Binary to Decimal Conversion: Binary numeral system: 1 is ON and 0 is OFF. 0s don't matter. 1s only matter so add the 2^placeValue values. So 1001011 is 75 in binary. Read from right to left.

Binary Number:             1     0     0     1     0     1     1
Place Value:               6     5     4     3     2     1     0
2 power Place Value:       2^6   2^5   2^4   2^3   2^2   2^1   2^0
Solve the above:           64    32    16    8     4     2     1

Add the 1 bit values:      64 + 8 + 2 + 1 = 75

Also notice that each time we add another binary digit we double the possible values.

Number of Digits     Formula     Settings
3                    2^3         8
4                    2^4         16
5                    2^5         32
6                    2^6         64

binary operator: needs 2 operands
Unary operator: single operand
Signed
Unsigned
one’s complement
2’s complement
Bitwise AND (&): Binary operator. returns bit by bit AND of i/p values. if both bits 1 then gives 1 else 0
Bitwise OR (|): Binary operator. returns bit by bit OR of i/p values. if either bits is 1 then 1 else 0.
Bitwise XOR (^): Binary operator. return bit by bit XOR of i/p values. if both bits same then 0 else 1
Bitwise NOT (~): Unary operator. returns 1s complement representation of i/p values. all bits inverted. every 0 to 1 n every 1 to 0.
Shift Operators: They shift bits of nums left or right thereby multiplying or dividing the num by 2. They can be used when we have to multiply or divide a number by two. Ex: 6 >> 3. This can be read as "shift the binary digits of the decimal value 6 by 3 positions to the right". 6 in binary is 000...0110 and shifting 3 positions to the right means?
Signed Right Shift (>>): Right shifting is division by 2.
Unsigned Right Shift (>>>):
Signed Left Shift (<<): Left shifting is multiply by 2. this means shift the binary value of 6 left by 5 positions.
Unsigned Left Shift (<<):
Logical (<<) and arithmetic left-shift (<<<) operations are same in java.
On Mac you have this wonderful Programmer Calculator. Open Calculator > View > Programmer or Cmd + 3. You can perform all your bitwise operations here.

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instant-java's Introduction

Code Snippets Java 8

Package definition and imports

Comments

Printing to Console

Data Types

Constants and Variables

Operators

Conditionals

Loops

Collections

Bitwise Operations

Classes

Functions

Instantiation and Intitialization

Inheritance

Composition

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