java - 功能接口(interface)方法引用

Question

我是 Java 8 的新手，正在尝试这个。我有一个界面

public interface CurrencyRateDao{
    Double getCurrencyRate(String srcCur,String tarCur, int month);
}

以这种方式访问​​:

CurrencyRateDao currencyRateDao = new CurrencyRateDaoImpl();
Double rate = ('USD','INR',1) -> currencyRateDao::getCurrencyRate;

报错:

target type of this expression must be a functional interface.

请指出上面的代码有什么问题

Answer 1

你只需要

Double rate = currencyRateDao.getCurrencyRate("USD", "INR", 1);

如果您将接口(interface)表示为 lambda，它看起来像:

CurrencyRateDao currencyRateDao = (srcCur, tarCur, month) -> Double.MAX_VALUE;
// accepts three arguments and returns a Double value