《Java语言程序设计(基础篇)》(第10版 梁勇 著)第八章练习题答案

《Java语言程序设计（基础篇）》（第10版梁勇著）

第八章练习题答案

8.1

public class Exercise08_01 {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

System.out.print("Enter a 3 by 4 matrix row by row: ");

double[][] m = new double[3][4];

for (int i = 0; i < m.length; i++)

for (int j = 0; j < m[i].length; j++)

m[i][j] = input.nextDouble();

for (int j = 0; j < m[2].length; j++) {

System.out.println("Sum of the elements at column " + j + " is " + sumColumn(m, j));

}

}

public static double sumColumn(double[][] m, int columnIndex) {

double total = 0;

for (int i = 0; i < m.length; i++)

total += m[i][columnIndex];

return total;

}

}

8.1附加

public class Exercise08_01Extra {

public static void main(String[] args) {

final int N = 2;

Scanner input = new Scanner(System.in);

double[][] A = new double[N][N];

System.out.print("Enter a, b, c, d: ");

A[0][0] = input.nextDouble();

A[0][1] = input.nextDouble();

A[1][0] = input.nextDouble();

A[1][1] = input.nextDouble();

double[][] inverseA = inverse(A);

if (inverseA == null)

System.out.println("No inverse matrix");

else

printMatrix(inverse(A));

}

public static void printMatrix(double[][] A) {

for (int i = 0; i < A.length; i++) {

for (int j = 0; j < A.length; j++)

System.out.print(A[i][j] + " ");

System.out.println();

}

}

public static double[][] inverse(double[][] A) {

double[][] result = new double[A.length][A.length];

double determinant = A[0][0] * A[1][1] - A[0][1] * A[1][0];

if (determinant == 0)

return null;

result[0][0] = A[1][1] / determinant;

result[0][1] = -A[0][1] / determinant;

result[1][0] = -A[1][0] / determinant;

result[1][1] = A[0][0] / determinant;

return result;

}

}

8.2

public class Exercise08_02 {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

System.out.print("Enter a 4 by 4 matrix row by row: ");

double[][] m = new double[4][4];

for (int i = 0; i < 4; i++)

for (int j = 0; j < 4; j++)

m[i][j] = input.nextDouble();

System.out.print("Sum of the elements in the major diagonal is "

+ sumMajorDiagonal(m));

}

public static double sumMajorDiagonal(double[][] m) {

double sum = 0;

for (int i = 0; i < m.length; i++)

sum += m[i][i];

return sum;

}

}

8.2附加

public class Exercise08_02Extra {

final static int N = 3;

public static void main(String[] args) {

double[][] A = new double[N][N];

System.out.print("Enter a11, a12, a13, a21, a22, a23, a31, a32, a33: ");

Scanner input = new Scanner(System.in);

A[0][0] = input.nextDouble();

A[0][1] = input.nextDouble();

A[0][2] = input.nextDouble();

A[1][0] = input.nextDouble();

A[1][1] = input.nextDouble();

A[1][2] = input.nextDouble();

A[2][0] = input.nextDouble();

A[2][1] = input.nextDouble();

A[2][2] = input.nextDouble();

System.out.print("Enter b1, b2, b3: ");

double[] B = new double[3];

B[0] = input.nextDouble();

B[1] = input.nextDouble();

B[2] = input.nextDouble();

double[] result = getSolution(A, B);