1. תרגול 3
שיטות ומערכים

2. מערך כ reference-
public static void ChangeArray() { int [] array1={1,1}; int [] array2=array1; array1[0]=2; System.out.println("Array2=["+array2[0]+","+array2[1]+"]"); }
Array2=[2,1]

3. מערך כ reference-
public static void ArrayComparison() { int [] array1={1,1}; int [] array2={1,1}; if (array1==array2){ System.out.println(“array1 ==array2");} else{ System.out.println(“array1 != array2");} }
array1 != array2"

4. Methods/functions
public/private/protected static < return type > < name > (parameters list)
משמש ליצירת שיטת מחלקה
טיפוס הערך המוחזר ע"י השיטה
בקרת גישה לשיטה
(encapsulation)
שם השיטה
המשתנים שהשיטה מקבלת
private
protected
Public
מאותה מחלקה כן
מכל מחלקה הנמצאת באותה חבילה לא
מכל מחלקה הנמצאת מחוץ לחבילה
מתת מחלקה הנמצאת באותה חבילה
מתת מחלקה הנמצאת מחוץ לחבילה

5. Method parameters
public static int [][] CopyMatrix(int [][] array1){ int [][] array2; int N= array1.length; int M= array1[0].length; array2=new int [N][M]; for(int i=0;i<N;i++) for(int j=0;j<M;j++) {array2[i][j]=array1[i][j];} return array2; } public static void main(String[] args) { int [][] array1={{2,2},{3,2}}; int [][] array2=new int [2][2]; array2=CopyMatrix(array1);

6. Method parameters
public static int [][] CopyMatrix(int [][] array1){ int [][] array2; int N= array1.length; int M= array1[0].length; array2=new int [N][M]; for(int i=0;i<N;i++) for(int j=0;j<M;j++) {array2[i][j]=array1[i][j];} return array2; } public static void main(String[] args) { int [][] array1={{2,2},{3,2}}; array2=CopyMatrix(array1);

7. Method parameters
public static void CopyMatrix(int [][] array1,int [][] array2){ int N= array1.length; int M= array1[0].length; for(int i=0;i<N;i++) for(int j=0;j<M;j++) {array2[i][j]=array1[i][j];} } public static void main(String[] args) { int [][] array1={{2,2},{3,2}}; int [][] array2; array2=new int[2][2]; CopyMatrix(array1,array2);

8. Method overloading public int a(int x) { } public int a(int x, int y)
public double a(int x, int y)

9. דוגמה בנה תוכנית המבצעת את הפעולות הבאות: מכפלת וקטור בוקטור
מכפלת וקטור במטריצה
מכפלת מטריצה במטריצה

10. Matrix vector multiplication
C=A*B
Res
Vector
Vector
a(1,2)
a(1,1)
a(2,2)
a(2,1)
a(3,2)
a(3,1)
c(1,1)
c(2,1)
c(3,1)
Mat[0]
b(1,1)
b(2,1) X
Mat[1] =
Mat[2]

11. Matrix multiplication
C=A*B
res
Mat[0]
res
Mat[1]
res
Mat[2]
Mat2[0]
Mat2[1]
Mat2[2]
c(1,3)
c(1,2)
c(1,1)
c(2,3)
c(2,2)
c(2,1)
c(3,3)
c(3,2)
c(3,1)
a(1,2)
a(1,1)
a(2,2)
a(2,1)
a(3,2)
a(3,1)
Mat1[0]
b(1,3)
b(1,2)
b(1,1)
b(2,3)
b(2,2)
b(2,1) = X
Mat1[1]
Mat1[2]

12. Matrix vector multiplier
מבנה התוכנית
menu
Matrix multiplier
Matrix vector multiplier
Vector multiplier

13. /**
* This method calculate vector multiplication ([1xM]*[Mx1])
vector1- An 1xM double array holds the multiplicand vector.
vector2- An Mx1 double array holds the multiplier vector.
res- A double scalar holds the vector product result. */
public static double VectorMult( double[] vector1, double[] vector2)
/**
* This method calculate matrix by vector multiplication ([NxM]*[Mx1])
matrix- An NxM double array holds the multiplicand matrix
vector- An Mx1 double array holds the multiplier vector
resVector- The Nx1 double array holds the product result. */
public static double[] MatrixVectorMult( double[][] matrix,double[] vector)
/**
* This method calculate matrix multiplication ([NxM]*[MxN])
matrix1- An NxM double array holds the multiplicand matrix
matrix2- An NxM double array holds the transpose of the multiplier matrix
resMat- The NxN double array holds the product result. */
public static double[][] MatrixMult(double[][] matrix1,double[][] matrix2)
/**
* This method calculate matrix transpose
matrix- An NxM double array holds the matrix to be transpose.
matrixTranspose- An MxN double array holds matrix transpose. */
private static double[][] MatrixTranspose(double[][] matrix)

14. /**
* This method calculate vector multiplication ([1xM]*[Mx1])
vector1- An 1xM double array holds the multiplicand vector.
vector2- An Mx1 double array holds the multiplier vector.
res- A double scalar holds the vector product result. */
public static double VectorMult( double[] vector1, double[] vector2) {
int M=vector1.length;
double res=0;
for (int m=0;m< M;m++) //run in loop on vectors entry.
res +=vector1[m]*vector2[m]; }
return res;

15. /**
* This method calculate matrix by vector multiplication ([NxM]*[Mx1])
matrix- An NxM double array holds the multiplicand matrix
vector- An Mx1 double array holds the multiplier vector
resVector- The Nx1 double array holds the product result. */
public static double[] MatrixVectorMult( double[][] matrix,double[] vector) {
int N= matrix.length; //matrix number of rows
int M= vector.length; //matrix number of column
double[] resVector= new double[M];
for (int n=0;n< N;n++)// run in loop on matrix rows
resVector[n] =VectorMult(matrix[n],vector); }
return resVector;

16. /**
* This method calculate matrix multiplication ([NxM]*[MxN])
matrix1- An NxM double array holds the multiplicand matrix
matrix2- An NxM double array holds the transpose of the multiplier matrix
resMat- The NxN double array holds the product result. */
public static double[][] MatrixMult(double[][] matrix1,double[][] matrix2 {
int N=matrix1.length; //multilicand matrix number of rows
matrix2=MatrixTranspose(matrix2);
double[][] resMat=new double[N][];
for (int i=0;i< N;i++) //run in loop on matrix rows
resMat[i]=MatrixVectorMult(matrix1,matrix2[i]); }
resMat=MatrixTranspose(resMat);
return resMat;

17. /**
* This method calculate matrix transpose
matrix- An NxM double array holds the matrix to be transpose.
matrixTranspose- An MxN double array holds matrix transpose. */
private static double[][] MatrixTranspose(double[][] matrix) {
double[][] matrixTranspose;
int N=matrix.length;
int M=matrix[0].length;
matrixTranspose= new double[M][N];
for (int n=0;n< N;n++)
for(int m=0;m< M;m++)
matrixTranspose[m][n]=matrix[n][m]; }
return matrixTranspose;