将一个double值数组从一个java类传递给另一个java类

Question

I have an Java class file that contains an array of double values that I wanted to use in another Java class file. This is the simplified version of my code:

File1.java

public class File1.java{

//code

public void compute
{
    double[] vectorX_U = {0.1, 0.2, 0.5}
}

//i tried this method to pass but it said vectorX_U cannot be resolved to a variable
 public Double[] getvectorX_U() 
 {
     return vectorX_U;
 }

File2.java

//i attempt to use the array
public void computethis
{
    File1 td = new File1();
    System.out.println(td.getvectorX_U());
}

Can I have some help on how to achieve this? Thanks!

Answer 1

Your File1 is riddled with errors.

Basically (besides the compilation errors), you need to have your array of doubles as an instance variable.

As it is now, it is a local variable within the compute method, and your get method has no access to it.

File1.java

public class File1{ // no .java here!

double[] vectorX_U;

public void compute
{
    vectorX_U = {0.1, 0.2, 0.5}
}


 public Double[] getvectorX_U() 
 {
     return vectorX_U; // now it will find the instance variable
 }
}

EDIT:

you will need to call the compute method before calling the getvectorX_U, though. If you don't, the array will not be initialized, and the getter will return null.

Answer 2

if you don`t want change the arrays value and all the class can use it as "global variable" you can set

public class File1.java{

   public static final double[] VECTORX_U = {0.1, 0.2, 0.5};

   ............

}

if you want change it and every this variable in instances are same

public class File1.java{

   static double[] vectorX_U = {0.1, 0.2, 0.5};

   ............

}

if variable in every instance of this class has a special value

public class File1.java{

   double[] vectorX_U = {0.1, 0.2, 0.5};

   ............

}

for the first and second you can use File1.variable ,the third you need create a instance of this class then you can use it

Answer 3

Basically your vectorX_U variable's scope is inside the compute method. So non of other methods can access the vectorX_U variable. so it should be a global variable.