UJCS | Ultimate Java Cheat Sheet

int i = 5, j;
int a = 3, b = a + 1;
final int c; //=> Constant
c = 22; // may be init after

// Single Line
/\* Multi Line \*/
/\*\* Docu String \*/

int[] a; //Declaration
a = new int[5] //Dimension
int[] a = new int[5];
int[] b = {10, 20, 30};

int[][] matrix = new int[2][3];

int[] a;
a.length;     //length of array

ArrayList<Double> nums = new ArrayList<>();
nums.add(2.3);
nums.size() == 1
double a = nums.get(0);

int a, b;
a = (double) b * a    //b => double
a = b * (double) a    //a => double

a = (double) (a * b)
/\* (a * b) will be calculated 
with int logic then 
type-casted to double \*/

File file = new File("text.txt");

file.exsits();
file.createNewFile();
file.delete();

BufferdReader = new BufferedReader(file);
while ((line = input.readLine()) != null) {
 //statements with line
}

// Pop-Up Box:
import javax.swing.*;
String out = JOptionPane.showInputDialog("Inp: ");

Pattern p = Pattern.compile("\\w+");
Matcher m = p.matcher("abc");

while (m.find()) {
    m.group()
}

//true if whole string matches
m.matches() -> bool

//**Syntax for a standalone application in Java:**
class <classname>
{
      public static void main(String args[])  {
          statements;
          ————————;
          ————————;
      }
}

**If Statem­ent**
if ( expre­ssion ) {
 ­ ­st­ate­ments
} else if ( expre­ssion ) {
 ­ ­st­ate­ments
} else {
 ­ ­st­ate­ments
}

**While Loop**
while ( expre­ssion ) {
 ­ ­st­ate­ments
}

**Do-While Loop**
do {
 ­ ­st­ate­ments
} while ( expre­ssion );

**For Loop**
for ( int i = 0; i < max; ++i) {
 ­ ­st­ate­ments
}

**For Each Loop**
for ( vartype var : colle­ction ) {
 ­ ­st­ate­ments
}

**Switch Statem­ent**
switch ( expre­ssion ) {
 ­ case value:
 ­ ­ ­ ­st­ate­ments
 ­ ­ ­ ­break;
 ­ case value2:
 ­ ­ ­ ­st­ate­ments
 ­ ­ ­ ­break;
 ­ ­def­ault:
 ­ ­ ­ ­st­ate­ments
}

**Exce­ption Handling**
try {
 ­ ­sta­tem­ents;
} catch (Exce­pti­onType e1) {
 ­ ­sta­tem­ents;
} catch (Exception e2) {
 ­ ­cat­ch-all statem­ents;
} finally {
 ­ ­sta­tem­ents;
}