如何在Java中使用函数列表来比较两个对象的字段并求和结果

Question

我有两个对象可以一个字段一个字段地比较，对函数列表中的每个字段使用不同的函数。

public class NeedCompare {
private BigDecimal category;
private String name;
private BigDecimal value;
private BigDecimal amount;

// The list is wrong and I don't know how to organize it
private List<Function<BigDecimal, NeedCompare>> functions = Arrays.asList(
        (needCompare1, needCompare2) -> compareCategory(needCompare1, needCompare2),
        (needCompare1, needCompare2) -> compareName(needCompare1, needCompare2),
        (needCompare1, needCompare2) -> compareValue(needCompare1, needCompare2),
        (needCompare1, needCompare2) -> compareAmount(needCompare1, needCompare2)

);

public BigDecimal compare(NeedCompare n1, NeedCompare n2) {
    //The method is broken. I need to return a sum of the results of the functions
    return functions.stream().map(function -> function(n1, n2)).reduce(BigDecimal.ZERO, BigDecimal::add);
}

private BigDecimal compareAmount(NeedCompare needCompare1, NeedCompare needCompare2) {
    // Complex function to compare category of NeedCompare
    return needCompare1.getCategory().equals(needCompare2.getCategory()) ? BigDecimal.ZERO : BigDecimal.ONE;
}

private BigDecimal compareValue(NeedCompare needCompare1, NeedCompare needCompare2) {
    // Complex function to compare name of NeedCompare
    return needCompare1.getName().equals(needCompare2.getName()) ? BigDecimal.ZERO : BigDecimal.ONE;
}

private BigDecimal compareName(NeedCompare needCompare1, NeedCompare needCompare2) {
    // Complex function to compare value of NeedCompare
    return needCompare1.getValue().equals(needCompare2.getValue()) ? BigDecimal.ZERO : BigDecimal.ONE;
}

private BigDecimal compareCategory(NeedCompare needCompare1, NeedCompare needCompare2) {
    // Complex function to compare amount of NeedCompare
    return needCompare1.getAmount().equals(needCompare2.getAmount()) ? BigDecimal.ZERO : BigDecimal.ONE;
}
// Getters and setters ...

Answer 1

您的函数有两个参数，所以它们是bifunction （首先是参数的类型，return/target类型是最后一个）。所以您有私有列表 >函数 。

此外，通过使用方法引用而不是lambdas，您可以简单地使列表更具可读性：

private List<BiFunction<NeedCompare, NeedCompare, BigDecimal>> functions 
    = Arrays.asList(this::compareCategory, this::compareName, 
        this::compareValue, this::compareAmount);