Calculate with Array

 


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

    int[] intArray = new int[] { 1, 2, 3, 4, 5 };
    // calculate sum
    int sum = 0;
    for (int i = 0; i < intArray.length; i++){
      sum = sum + intArray[i];
    }
    // calculate average
    double average = sum / intArray.length;

    System.out.println("average: " + average);
  }
}

 

average: 3.0

 
import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    int length = 20;
    long[] series = new long[length];
    series[0] = 0;
    series[1] = 1;
    for (int i = 2; i < length; i++) {
      series[i] = series[i - 1] + series[i - 2];
    }
    System.out.print(Arrays.toString(series));
  }
}

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181]

 
class Matrix {
  private double[][] doubleArray;

  Matrix(int nrows, int ncols) {
    doubleArray = new double[nrows][ncols];
  }

  int getCols() {
    return doubleArray[0].length;
  }

  int getRows() {
    return doubleArray.length;
  }

  double getValue(int row, int col) {
    return doubleArray[row][col];
  }

  void setValue(int row, int col, double value) {
    doubleArray[row][col] = value;
  }
}

public class Main {
  public static void main(String[] args) {
    Matrix a = new Matrix(1, 3);
    a.setValue(0, 0, 1); // | 1 2 3 |
    a.setValue(0, 1, 2);
    a.setValue(0, 2, 3);
    dump(a);
    Matrix b = new Matrix(3, 2);
    b.setValue(0, 0, 4); // | 4 7 |
    b.setValue(1, 0, 5); // | 5 8 |
    b.setValue(2, 0, 6); // | 6 9 |
    b.setValue(0, 1, 7);
    b.setValue(1, 1, 8);
    b.setValue(2, 1, 9);
    dump(b);
    dump(multiply(a, b));
  }

  static void dump(Matrix m) {
    for (int i = 0; i < m.getRows(); i++) {
      for (int j = 0; j < m.getCols(); j++){
        System.out.print(m.getValue(i, j) + " ");
      }
      System.out.println();
    }
    System.out.println();
  }

  static Matrix multiply(Matrix a, Matrix b) {
    if (a.getCols() != b.getRows()) {
      throw new IllegalArgumentException("rows/columns mismatch");
    }
    Matrix result = new Matrix(a.getRows(), b.getCols());
    for (int i = 0; i < a.getRows(); i++) {
      for (int j = 0; j < b.getCols(); j++) {
        for (int k = 0; k < a.getCols(); k++) {
          result.setValue(i, j, result.getValue(i, j) + a.getValue(i, k) * b.getValue(k, j));
        }
      }
    }

    return result;
  }
}