2. Types

2.1. Basic Types

byte b = 127;
short s = 32_767;
int i = 2_147_483_647;
long l = 9_223_372_036_854_775_807L;
float f = 3.4e38f;
double d = 1.7e308d;
char c = 'Z';
boolean o = true;
String t = "Hello, world!";

// wrapping the primitives into object types
Byte b = 127;
Short s = 32_767;
Integer i = 2_147_483_647;
Long l = 9_223_372_036_854_775_807L;
Float f = 3.4e38f;
Double d = 1.7e308d;
Character c = 'Z';
Boolean o = true;

// getting the primitives back
byte bb = b.byteValue();
short ss = s.shortValue();
int ii = i.intValue();
long ll = l.longValue();
float ff = f.floatValue();
double dd = d.doubleValue();
char cc = c.charValue();
boolean oo = o.booleanValue();

2.2. Arrays

int months[] = new int[12];

months[0] = 0;
months[1] = 1;
months[2] = 2;
months[3] = 3;
months[4] = 4;
months[5] = 5;
months[6] = 6;
months[7] = 7;
months[8] = 8;
months[9] = 9;
months[10] = 10;
months[11] = 11;

int months[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };

int matrix[][] = new int[2][2];
matrix[0][0] = 1;
matrix[0][1] = 2;
matrix[1][0] = 3;
matrix[1][1] = 4;

int matrix[][] = { {1, 2}, {3, 4} };

2.3. Type inference with var

var d = 10.0;
var s = "Hello, World!";
var b = true;
var a = new int[] { 0, 1, 2 };
var m = new int[][] { {1, 2}, {3, 4} };

2.4. String

2.4.1. String instantiation

String s1 = "Hello, world!";
String s2 = new String("Hello, world!");

var characters = new char[] {'H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '!'};
String s3 = new String(characters);
String s4 = new String(characters, 0, 5);

var ascii = new byte[] {72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33};
String s5 = new String(ascii);

2.4.2. String concatenation

var s1 = "Hi"; // basic string
var s2 = "Hello, I am " + " very hungry."; // string concatenation
var s3 = "I am " + String.format("%.2f", 55.555) + " inches tall."; // string formatting
var s4 = "Hello, ".concat("world!");
var s5 = String.join(",", "John", "Jack", "Mary");

2.4.3. String comparison

String s1 = "Hello, world!";
String s2 = new String("Hello, world!");
String s3 = "hello, world!";

// equals and equalsIgnoreCase
System.out.println(s1.equals(s2));
System.out.println(s1.equals(s3));
System.out.println(s1.equalsIgnoreCase(s3));

// equals vs ==
System.out.println(s1 == s1);
System.out.println(s1 == s2);

// regionMatches
System.out.println(s1.regionMatches(0, s2, 0, 5));
System.out.println(s1.regionMatches(0, s3, 0, 5));
System.out.println(s1.regionMatches(true, 0, s3, 0, 5));

// startsWith and endsWith
System.out.println(s1.startsWith("Hello"));
System.out.println(s1.startsWith("hello"));

System.out.println(s1.endsWith("world!"));
System.out.println(s1.endsWith("World!"));

// compareTo
System.out.println(s1.compareTo(s2));
System.out.println(s1.compareTo(s3));

2.4.4. String extraction

String s = "Hello, world!";

var c = s.charAt(0);

var buffer = new char[5];
s.getChars(0, 5, buffer, 0);

var bytes = s.getBytes();

var sub1 = s.substring(0, 5);
var sub2 = s.substring(8);

2.4.5. String modification

String s = " Hello, world! ";

System.out.println(s.trim());
System.out.println(s.strip());
System.out.println(s.replace('o', 'a'));
System.out.println(s.replaceAll("o", "a"));
System.out.println(s.toLowerCase());
System.out.println(s.toUpperCase());

2.4.6. String search

String s1 = "Hello, world!";

System.out.println(s1.indexOf("Hello"));
System.out.println(s1.indexOf('e'));
System.out.println(s1.lastIndexOf("o"));

2.4.7. Getting an object’s string value

Byte b = 127;
Short s = 32_767;
Integer i = 2_147_483_647;
Long l = 9_223_372_036_854_775_807L;
Float f = 3.4e38f;
Double d = 1.7e308d;
Character c = 'Z';
Boolean o = true;

String bb = String.valueOf(b);
String ss = String.valueOf(s);
String ii = String.valueOf(i);
String ff = String.valueOf(f);
String dd = String.valueOf(d);
String cc = String.valueOf(c);
String oo = String.valueOf(o);

bb = b.toString();
ss = s.toString();
ii = i.toString();
ff = f.toString();
dd = f.toString();
cc = c.toString();
oo = c.toString();