Question

我遇到了一个从Octave调用Java库的奇怪问题。我正在使用http://www.json.org/java/中的JSON库。这是一个示例Java类：

import org.json.JSONObject;

public class Test {
  public static void main(String[] args) throws Exception {
    JSONObject obj = new JSONObject();
    obj.put("primitive", 3.1415926);
    obj.put("wrapped", new java.lang.Double(3.1415926));
    System.out.println(obj.toString());
  }
}

和Octave中的相应代码（我使用的是3.8.1）：

function test()
  javaaddpath('json.jar')
  obj = javaObject('org.json.JSONObject');
  obj.put('primitive', 3.1415926);
  obj.put('wrapped', javaObject('java.lang.Double', 3.1415926));
  disp(obj.toString());
end

当我编译并运行Java代码时，我当然得到了

{"wrapped":3.1415926,"primitive":3.1415926}

使用Octave，在我的OS X笔记本电脑上，我得到同样的东西。

$ octave --eval test
warning: function ./test.m shadows a core library function
GNU Octave, version 3.8.1
Copyright (C) 2014 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  For details, type 'warranty'.

Octave was configured for "x86_64-apple-darwin14.0.0".

Additional information about Octave is available at http://www.octave.org.

Please contribute if you find this software useful.
For more information, visit http://www.octave.org/get-involved.html

Read http://www.octave.org/bugs.html to learn how to submit bug reports.
For information about changes from previous versions, type 'news'.

{"primitive":3.1415926,"wrapped":3.1415926}

但是在我的Ubuntu 12.04 VM上，从ppa:octave/stable安装了Octave，我得到了：

$ octave --eval test
warning: function ./test.m shadows a core library function
GNU Octave, version 3.8.1
Copyright (C) 2014 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  For details, type 'warranty'.

Octave was configured for "i686-pc-linux-gnu".

Additional information about Octave is available at http://www.octave.org.

Please contribute if you find this software useful.
For more information, visit http://www.octave.org/get-involved.html

Read http://www.octave.org/bugs.html to learn how to submit bug reports.
For information about changes from previous versions, type 'news'.

{"wrapped":3,"primitive":3.1415926}

不知何故，java.lang.Double对象变为整数，或者至少小数部分被剥离。这是怎么回事？

使用双参数从Octave调用Java会丢失精度

0 个答案: