Java导入外部库:ApacheCommons数学

Question

在看了许多讨论之后，例如：

• Install commons math library for java in Ubuntu
• Correctly Importing Apache Commons Math Package

我仍然被困住了，无法使下列代码工作：

    import org.apache.commons.math3.linear;

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


    // Create a real matrix with two rows and three columns, using a factory
    // method that selects the implementation class for us.
    double[][] matrixData = { {1d,2d,3d}, {2d,5d,3d}};
    RealMatrix m = MatrixUtils.createRealMatrix(matrixData);

    // One more with three rows, two columns, this time instantiating the
    // RealMatrix implementation class directly.
    double[][] matrixData2 = { {1d,2d}, {2d,5d}, {1d, 7d}};
    RealMatrix n = new Array2DRowRealMatrix(matrixData2);

    // Note: The constructor copies  the input double[][] array in both cases.

    // Now multiply m by n
    RealMatrix p = m.multiply(n);
    System.out.println(p.getRowDimension());    // 2
    System.out.println(p.getColumnDimension()); // 2

    // Invert p, using LU decomposition
RealMatrix pInverse = new LUDecomposition(p).getSolver().getInverse();

    }
}

下面是我一步一步地做的事情。

首先，我使用

sudo apt-get install libcommons-math3-java

然后我查看了Common-math3-java安装的位置。

dpkg -L libcommons-math3-java 
/.
/usr
/usr/share
/usr/share/maven-repo
/usr/share/maven-repo/org
/usr/share/maven-repo/org/apache
/usr/share/maven-repo/org/apache/commons
/usr/share/maven-repo/org/apache/commons/commons-math3
/usr/share/maven-repo/org/apache/commons/commons-math3/3.2
/usr/share/maven-repo/org/apache/commons/commons-math3/3.2/commons-math3-3.2.pom
/usr/share/maven-repo/org/apache/commons/commons-math3/debian
/usr/share/maven-repo/org/apache/commons/commons-math3/debian/commons-math3-debian.pom
/usr/share/doc
/usr/share/doc/libcommons-math3-java
/usr/share/doc/libcommons-math3-java/changelog.Debian.gz
/usr/share/doc/libcommons-math3-java/copyright
/usr/share/java
/usr/share/java/commons-math3.jar
/usr/share/maven-repo/org/apache/commons/commons-math3/3.2/commons-math3-3.2.jar
/usr/share/maven-repo/org/apache/commons/commons-math3/debian/commons-math3-debian.jar
/usr/share/java/commons-math3-3.2.jar

然后我使用了(正如Install commons math library for java in Ubuntu中所讲的)

javac -cp .:/usr/share/java/commons-math3-3.2.jar linearAlgebraLearning.java 

但是，我仍然是一个导入错误消息：

linearAlgebraLearning.java:1: error: cannot find symbol
import org.apache.commons.math3.linear;

和额外的错误，因为编译器找不到类(如RealMatrix)。我知道这类问题已经问过很多次了。这里的人可能厌倦了这个问题..。但如果你能帮我我会很高兴的。

Ps :因为我的linux发行版上有Eclipse的一些bug，所以我不使用IDE，而是使用gedit和终端。

Answer 1

我首先安装了每个libcommons包：

sudo apt install libcommons\*

然后设置类路径：

export CLASSPATH="/usr/share/java/commons-math3.jar:/usr/share/java/commons-lang3.jar"

您的java应该会自动地捡起它。我用jshell测试了它，它能够自动完成/导入BlockRealMatrix，例如：

jshell> import org.apache.commons.math3.linear.BlockRealMatrix
jshell> BlockRealMatrix foo = new BlockRealMatrix(2, 2);
foo ==> BlockRealMatrix{{0.0,0.0},{0.0,0.0}}