创建自定义BigDecimal类型 [英] Creating a custom BigDecimal type

问题描述

在我的应用程序中，所有BigDecimal数字都按比例缩放以具有两位小数位.换句话说，每次我在代码中创建一个新的BigDecimal时，我也需要使用方法scale:

In my application, all BigDecimal numbers are scaled to have two decimal places.. In other words, everytime I create a new BigDecimal in my code, I need to use the method scale too:

BigDecimal x = BigDecimal.ZERO;
x.setScale(2, RoundingMode.HALF_UP);

因此，为了减少工作量，我想创建自己的自定义BigDecimal类型，例如:

So, to minimize the work, I wanted to create my custom BigDecimal type, something like:

public class CustomBigDecimal extends BigDecimal {

    public CustomBigDecimal(String val) {
        super(val);
        this.setScale(2, RoundingMode.HALF_UP);
    }

}

我知道this.setScale(2, RoundingMode.HALF_UP);不能完成这项工作，但是我找不到解决方法，有可能吗?

I know this.setScale(2, RoundingMode.HALF_UP); doesn't do the job, but I can't find the way to do it, is it possible?

推荐答案

您可以创建从BigDecimal扩展的CustomBigDecimal.但是，由于BigDecimal是不可变的，因此您永远不会从父类继承状态(例如缩放和舍入模式).

You could create a CustomBigDecimal that extends from BigDecimal. However, as BigDecimal is immutable, you would never inherit state (such as the scale and rounding mode) from the parent class.

我会去寻找另一个答案中建议的实用程序类，或者是将每个操作委派给实际BigDecimal实例的包装器.这种方法的缺点是您全新的CustomBigDecimal不会是BigDecimal，因此它们将不能互换.

I'd go for the utility class suggested in another answer, or maybe a wrapper that delegates every operation to an actual BigDecimal instance. The downside of this approach is that your brand new CustomBigDecimal wouldn't be a BigDecimal, so they wouldn't be interchangeable.

此方法的缺点是您必须委派大约50种方法.拥有出色的IDE并不是世界末日，但绝对不是很吸引人...

a downside of this approach is that you have to delegate about 50 methods. Not the end of the world with a good IDE, but definitely not very appealing...

如果毕竟您仍然想使CustomBigDecimal从BigDecimal继承，则需要使用 decorator 方法:

If, after all, you still want to make CustomBigDecimal inherit from BigDecimal, you'd need to use a decorator approach:

public class CustomBigDecimal extends BigDecimal {

    private final BigDecimal value;

    private CustomBigDecimal(BigDecimal value) {
        super(value.toPlainString()); // needed to compile, 
                                      // useless except for implicit null-check
        this.value = value;
    }

    public CustomBigDecimal(String val) {
        this(new BigDecimal(val).setScale(2, RoundingMode.HALF_UP));
    }

    @Override
    public CustomBigDecimal abs() {
        return new CustomBigDecimal(this.value.abs());
    }

    // TODO all other methods

}

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