primitive data types

int, double, char, ... are primitive (predefined) data types
arbitrary complex data types may be defined by the user
String is (however) an object, like everything else

Typ	Size	Domain
boolean	1	{true, false}
short	2
int	4	[−2³¹, 2³¹−1] =
long	8	[−2⁶³, 2⁶³−1]
float	4	[1.40239846 ⋅ 10^–45, 3.40282347 ⋅ 10³⁸]
double	8	[4.94065645841246544 ⋅ 10^–324, 1.79769131486231570 ⋅ 10³⁰⁸]

short / long for specialized applications only
float not used anymore, standard is
double for floating point operations
32/64 bits (int/double) used for memory addressing by 32/64 bit processors,
$\rightarrow$ memory restrictions

example: primitive data types

casting of one data type to another will be disussed later

public class PrimitiveDataTypes {

  public static void main(String[] args)
    {

// --- pi with double (16 digits) and float (8 digits)
// --- Math.PI is a double constant
    double double_PI = Math.PI;
    float   float_PI = (float)Math.PI;    // casting double to float
   
    System.out.printf("pi with double: %24.20f\n",double_PI);
    System.out.printf("pi with  float: %24.20f\n",float_PI);
    System.out.printf("%25s ^\n","");   // pointer 
    System.out.println(" ");            // empty line

// --- int and long integer numbers
    int   int_int = 1;
    long long_int = 1;

    for (int i=0; i<34; i++)
      {
       int_int =   int_int * 2;
      long_int =  long_int * 2;
      System.out.printf("i+1, short, int, long: %4d %12d %12d\n",
                         i+1, int_int, long_int);
      }

    }
}

strings

a string (word) is an aribitrary sequence of characters
the String class java.lang.String
has many built-in member functions for string manipulation
String concatenation with +


public class ExampleStrings {
  public static void main(String[] args) 
  {

// --- defining and printing
// --- toUpperCase() is a member function of the String class
  String cdde = "cdde";
  System.out.println("abc");
  System.out.println(cdde);
  System.out.println(cdde.toUpperCase());

// --- String concatenation with '+'
  System.out.println("abc" + " " + cdde);

// --- substring() is a member function of the String class
  String c  = "abc".substring(2,3);
  String dd = cdde.substring(1,3);
  System.out.println(" c: " + c);
  System.out.println("dd: " + dd);

// --- valueOf() casts numbers into strings
  System.out.println(String.valueOf(Math.PI));

  } // end of ExampleStrings.main()
} // end of class ExampleStrings

casting vs parsing

here: conversion of primitive data types and strings
later: casting of objects

import java.util.*;
import java.math.*;

public class CastingDemo {

public static void main(String args[]) {

   double rr = Math.random();
   String ss = String.valueOf(rr);         // converting double into string
   System.out.println("a random number as a string: " + ss);
   System.out.printf( "                   and back: %f\n\n",
              Double.parseDouble(ss));     // parsing
//
   int ii = (int)(Math.random()*100.0);    // casting double into int
   System.out.printf( " random integer and string : %d %s\n",
              ii, String.valueOf(ii));

  }  // end of CastingDemo.main()
}    // end of CastingDemo

arrays

n-component array
```
int[] array = new int[n];
```
value of array-component k
```
int b = array[k];
```
array with predefined values
```
int[] array = {1, 2, 3};
```
length n of array
```
int b = array.length;
```
multi-dimensional arrays
```
int[][] array = new int[n][m];
```

example: arrays

arrays start always with [0]

public class ExampleArrays {
  public static void main(String[] args) {

// --- array of integers
    int[] values = {2, 3, 5, 7, 11, 13};
    System.out.println(values[3]);     // 7

// --- array of strings
    String[] colors = {"yellow", "red", "green", "blue"};
    colors[0] = "black";
    for (int i=0; i<colors.length; i++)
      System.out.printf("This is color[%d]: %s \n", i, colors[i]);
    System.out.println(" ");           // empty line

// --- splitting a string, typically used when reading from file
    String inputString = "age height weight";
    String[] words = inputString.split(" ");
    for (int i=0; i<words.length; i++)
      System.out.printf("This is words[%d]: %s \n", i, words[i]);
    System.out.println(" ");           // empty line

// --- array of chars
  char[] chars = "black sun".toCharArray();
    for (int i=0; i<chars.length; i++)
      System.out.printf("This is chars[%d]: %c \n", i, chars[i]);
  }
}

example: matrices

matrix.length: the number of rows
matrix[i].length: the number of elements in row[i]
the number of elements per row may be variable (ragged matrix)

public class ExampleMatrices {
  public static void main(String[] args) 
  {

// --- defining a 3x2 matrix (3 rows and 2 columns)
  String[][] strMatrix = new String[3][2];
  String[] rowZero = { "rowZero[0]", "rowZero[1]"};
  String[] rowOne  = { "rowOne[0]", "rowOne[1]"};
  strMatrix[0] = rowZero;             // setting row [0]
  strMatrix[1] = rowOne;               // setting row [1]

// --- printing matrix
// --- note: row[2] is undefined (null)
  for (int i = 0; i<strMatrix.length; i++)
    for (int j = 0; j<strMatrix[i].length; j++)
      System.out.printf("  strMatrix[%d][%d]:  %s\n",
                         i, j, strMatrix[i][j]);
  System.out.println(" ");

// --- a matrix needs not to be rectangular, may be ragged
  int[][] intMatrix = new int[3][];    // allocate the number of rows
  int[] row_0 = {0,1,2,3,4};
  int[] row_1 = {5,6,7};
  int[] row_2 = {8,9};
  intMatrix[0] = row_0;
  intMatrix[1] = row_1;
  intMatrix[2] = row_2;

  for (int i = 0; i<intMatrix.length; i++)
    {
    System.out.printf("  strMatrix[%d]:",i);
    for (int j = 0; j<intMatrix[i].length; j++)
      System.out.printf(" %d",intMatrix[i][j]);
    System.out.printf("\n");
    }

  } // end of ExampleMatrices.main()
} // end of class ExampleMatrices

exercise: matrix operations

training suggestion
write a code for calculating the scalar product between two vectors
and for matrix multiplication

n × m-Matrix
```
int[][] matrix = new int[n][m];
```
value of M_ij
```
matrix[i][j]
```

initialize matrix with predefined values

int[][] matrix = new int[][] {{1, 2, 3}, {4, 5, 6}};

write a code for evaluating the trace of a given matrix

tr(M) ≔ ∑_i M_ii

arithmetic operators

assignment and arithmetics

Symbol	Description	Examples
=	assignment	`int i=5;`
+ -	addition, subtraction	`int i=5+3; int i=5-3;`
* /	multiplication, integer division	`int i=5*3; int i=9/3;`
%	modulo	`int i=14%3;`
+ -	unary plus/minus	`int i=+3; int i=-2;`
+= -= *= /=	assignment and operation	`i += 5;` // i = i + 5
++ --	pre-/postfix increment/decrement	`i++;` // i = i + 1

naming of C++

mathematical functions

import for basic mathematics

import java.lang.Math;

π ≈ 3.14159265358979323846
e ≈ 2.7182818284590452354, Euler's number
```
static final double PI;
static final double E;
```
absolute value |x|
```
static int abs(int x);
```

minimum/maximum value

static int min(int x, int y);
static int max(int x, int y);

(arcus-, hyperbolic-) sinus/cosine/tangent

static double sin(double x);
static double cos(double x);
static double tan(double x);
static double asin(double x);
static double acos(double x);
static double atan(double x);
static double hsin(double x);
static double hcos(double x);
static double htan(double x);

square/cubic root

static double sqrt(double x);
static double cbrt(double x);

exponential e^x
```
static double exp(double x);
```
power x^y
```
static double pow(double x, double y);
```

logarithm (base e/10)

static double log(double a);
static double log10(double a);

round

static double round(double a);
static long round(double a);

Programmierpraktikum

Java - Basic Data Types