java - 通过引用传递double值 [英] java - passing a double value by reference

问题描述

如何在java中通过引用传递double值？

how can I pass a double value by reference in java?

示例：

Double a = 3.0;
Double b = a;
System.out.println("a: "+a+" b: "+b);
a = 5.0;
System.out.println("a: "+a+" b: "+b);

此代码打印：

a: 3 b: 3
a: 5 b: 3

我的问题是让它打印出来：

and my problem is to get it to print:

a: 3 b: 3
a: 5 b: 5

我的目标：
我正在jess写一个专家系统，在那个应用程序中对于它的长度，segment将具有double值，现在double值不在单个段中;它存在于许多其他细分市场，比例类......等等，所有这些都引用它，等待它改变，以便它们可能符合一些规则。

my goal: I'm writing an expert system in jess, in that application a segment would have a double value for it's length, now that double value isn't in a single segment; it's in many other segments, proportionality classes..etc, all of which are referencing to it, waiting it to change so that they could possibly meet some rules.

如果我不能得到那个双倍更改，我不能有一个特定的规则fire包含一个引用该double值的对象。

if I can't get that double to change, I can't have a certain rule fire which contains an object that references to that double value.

推荐答案

Java不支持指针，所以你不能直接指向一个内存（如在C / C ++中）。

Java doesn't support pointers, so you can't point to a's memory directly (as in C / C++).

Java确实支持引用，但是引用只是对象的引用。无法引用本机（内置）类型。因此，当您执行时（自动装箱将您的代码转换为以下内容）。

Java does support references, but references are only references to Objects. Native (built-in) types cannot be referenced. So when you executed (autoboxing converted the code for you to the following).

Double a = new Double（3.0）;

Double a = new Double(3.0);

这意味着当你执行时

Double b = a;

您获得了对象的引用。当您选择更改a（自动装箱最终会将您的代码转换为此代码）

you gain a reference to a's Object. When you opt to change a (autoboxing will eventually convert your code above to this)

a = new Double(5.0);

这不会影响b对之前创建的 new Double（3.0）的引用）。换句话说，你不能通过直接操作（或者在Java中没有远处的动作）来影响b的引用。

Which won't impact b's reference to the previously created new Double(3.0). In other words, you can't impact b's reference by manipulating a directly (or there's no "action at a distance" in Java).

这就是说，还有其他解决方案

That said, there are other solutions

public class MutableDouble() {

   private double value;

   public MutableDouble(double value) {
     this.value = value;
   }

   public double getValue() {
     return this.value;
   }

   public void setValue(double value) {
     this.value = value;
   }
 }

 MutableDouble a = new MutableDouble(3.0);
 MutableDouble b = a;

 a.setValue(5.0);
 b.getValue(); // equals 5.0

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