有了前面的基础,现在理解这个还是轻松,不像前面的Huffman树。
1,矩阵对象的创建.
2,getRows 等: getter, setter 在 java 里面很常用. 主要是为了访问控制.
3,整数矩阵的加法、乘法.
4,Exception 的抛出与捕获机制.
5,用 this 调用其它的构造方法以减少冗余代码.
6,代码看起来多, 但矩阵运算我们以前写过(其实去掉注释也就只有100多行).
7,把数据类型修改成 double, 获得 DoubleMatrix.java, 以后会很有用.
8,getIdentityMatrix: 单位矩阵.
9,esultMatrix.data[i][i]: 成员变量的访问权限: 在同一类里面是可以直接使用的.
代码
package matrix;
import java.util.Arrays;
/**
* Int matrix. For efficiency we do not define ObjectMatrix. One can revise it to obtain DoubleMatrix.
*
* @author goudiyuan
*/
public class IntMatrix {
/**
* The data.
*/
int[][] data;
/**
* ***********************
* The first constructor
*
* @param paraRows
* The number of rows.
* @param paraColumns
* The number of columns.
* *************************
*/
public IntMatrix(int paraRows, int paraColumns) {
data = new int[paraRows][paraColumns];
}// Of the first constructor
/**
* ***********************
* The second constructor
*
* @param paraMatrix
* The given matrix.
* *************************
*/
public IntMatrix(int[][] paraMatrix) {
data = new int[paraMatrix.length][paraMatrix[0].length];
// Copy elements
for (int i = 0; i < data.length; i++) {
for (int j = 0; j < data[0].length; j++) {
data[i][j] = paraMatrix[i][j];
} // Of for j
} // Of for i
}// Of the second constructor
/**
* ***********************
* The third constructor. Construct a copy of the given matrix.
*
* @param paraMatrix
* The given matrix.
* *************************
*/
public IntMatrix(IntMatrix paraMatrix) {
this(paraMatrix.getData());
}// Of third constructor
/**
* **********************
* Get identity matrix. The values at diagonal are all 1.
*
* @param paraRows
* The given rows
****************************
*/
public static IntMatrix getIdentityMatrix(int paraRows) {
IntMatrix resultMatrix = new IntMatrix(paraRows, paraRows);
for (int i = 0; i < paraRows; i++) {
// According to access control, resultMatrix.data can be visited.
// directly.
resultMatrix.data[i][i] = 1;
} // Of for i
return resultMatrix;
}// Of getIdentityMatrix
/**
* ***********************
* Overrides the method claimed in Object, the superclass of all class.
* **********************
*/
public String toString() {
return Arrays.deepToString(data);
}// Of toString
/**
* *********************
* Get my data. Warning, the reference to the data instead of a copy of the data is returned.
*
* @return The data matrix.
* *********************
*/
public int[][] getData() {
return data;
}// Of getData
/**
* ***************
* Getter.
*
* @return The number of rows.
* ****************
*/
public int getRows() {
return data.length;
}// Of getRows
/**
* ***************
* Getter.
*
* @return The number of columns.
* ****************
*/
public int getColumns() {
return data[0].length;
}// Of getColumns
/**
* ***********************
* Set one the value of one element.
*
* @param paraRow
* The row of the element.
* @param paraColumn
* The column of the element.
* @param paraValue
* The new value.
* *************************
*/
public void setValue(int paraRow, int paraColumn, int paraValue) {
data[paraRow][paraColumn] = paraValue;
}// Of setValue
/**
* *********************
* Get the value of one element.
*
* @param paraRow
* The row of the element.
* @param paraColumn
* The column of the element.
* **********************
*/
public int getValue(int paraRow, int paraColumn) {
return data[paraRow][paraColumn];
}// Of getValue
/**
* *********************
* Add another matrix to me.
*
* @param paraMatrix
* The other matrix
* *********************
*/
public void add(IntMatrix paraMatrix) throws Exception {
// Step 1. Get the data of the matrix.
int[][] tempData = paraMatrix.getData();
// Step 2. Size check.
if (data.length != tempData.length) {
throw new Exception(
"Cannot add matrices. Rows not match: " + data.length + " vs. " + tempData.length + ".");
} // Of if
if (data[0].length != tempData[0].length) {
throw new Exception(
"Cannot add matrices. Rows not match: " + data[0].length + " vs. " + tempData[0].length + ".");
} // Of if
// Step 3. Add to me.
for (int i = 0; i < data.length; i++) {
for (int j = 0; j < data[0].length; j++) {
data[i][j] += tempData[i][j];
} // Of for j
} // Of for i
}// Of add
/**
* **********************
* Add two existing matrices.
* @param paraMatrix1
* The first matrix.
* @param paraMatrix2
* The second matrix.
* @return A new matrix.
* ***********************
*/
public static IntMatrix add(IntMatrix paraMatrix1, IntMatrix paraMatrix2) throws Exception {
// Step 1. Clone the first matrix
IntMatrix resultMatrix = new IntMatrix(paraMatrix1);
// Step 2. Add the second one.
resultMatrix.add(paraMatrix2);
return resultMatrix;
}// Of add
/**
* ********************
* Multiply two existing matrices.
*
* @param paraMatrix1
* The first matrix.
* @param paraMatrix2
* The second matrix.
* @return A new matrix.
* *********************
*/
public static IntMatrix multiply(IntMatrix paraMatrix1, IntMatrix paraMatrix2) throws Exception {
// Step 1.Check size.
int[][] tempData1 = paraMatrix1.getData();
int[][] tempData2 = paraMatrix1.getData();
if (tempData1[0].length != tempData2[0].length) {
throw new Exception("Cannot multiply matrices: " + tempData1[0].length + " vs. " + tempData2.length + ".");
} // Of if
// Step 2. Allocate space.
int[][] resultData = new int[tempData1.length][tempData2[0].length];
// Step 3. Multiply
for (int i = 0; i < tempData1.length; i++) {
for (int j = 0; j < tempData2[0].length; j++) {
for (int k = 0; k < tempData1[0].length; k++) {
resultData[i][j] += tempData1[i][k] * tempData2[k][j];
} // Of for k
} // Of for j
} // Of for i
// Step 4. Construct the matrix object.
IntMatrix resultMatrix = new IntMatrix(resultData);
return resultMatrix;
}// Of multiply
/**
* **********************
* The entrance of the program.
*
* @param args
* Not used now.
* ************************
*/
public static void main(String[] args) {
IntMatrix tempMatrix1 = new IntMatrix(3, 3);
tempMatrix1.setValue(0, 1, 1);
tempMatrix1.setValue(1, 0, 1);
tempMatrix1.setValue(1, 2, 1);
tempMatrix1.setValue(2, 1, 1);
System.out.println("The original matrix is: " + tempMatrix1);
IntMatrix tempMatrix2 = null;
try {
tempMatrix2 = IntMatrix.multiply(tempMatrix1, tempMatrix1);
} catch (Exception ee) {
System.out.println(ee);
} // Of try
System.out.println("The square matrix is: " + tempMatrix2);
IntMatrix tempMatrix3 = new IntMatrix(tempMatrix2);
try {
tempMatrix3.add(tempMatrix1);
} catch (Exception ee) {
System.out.println(ee);
} // Of try
System.out.println("The connectivity matrix is: " + tempMatrix3);
}// Of main
}// Of class IntMatrix
运行结果