我想使用 Java 8 新引入的函数对象将遗留方法部分应用于某些参数。
这里是有问题的方法:
/**
* Appends a {@code character} a couple of {@code times} to a {@code string}.
*
* @return the string with the appended characters as a StringBuilder
*/
private static StringBuilder appendChar(char character, int times, String string) {
StringBuilder strBuilder = new StringBuilder(string);
for (int i = 0; i < times; i++) {
strBuilder.append(character);
}
return strBuilder;
}
最佳答案
这实现了我想做的事情:
/*
* Pass two arguments. The created function accepts a String and
* returns a StringBuilder
*/
Function<String, StringBuilder> addEllipsis = appendToMe -> appendChar(
'.', 3, appendToMe);
/*
* Pass one argument. This creates a function that takes another two
* arguments and returns a StringBuilder
*/
BiFunction<String, Integer, StringBuilder> addBangs = (appendToMe,
times) -> appendChar('!', times, appendToMe);
// Create a function by passing one argument to another function
Function<String, StringBuilder> addOneBang = appendToMe -> addBangs
.apply(appendToMe, 1);
StringBuilder res1 = addBangs.apply("Java has gone functional", 2);
StringBuilder res2 = addOneBang.apply("Lambdas are sweet");
StringBuilder res3 = addEllipsis.apply("To be continued");
有关 Java 的所有预定义函数对象变体的列表,请查看 here .
编辑:
如果你有一个有很多参数的方法,你可以写你自己的函数:
/**
* Represents a function that accepts three arguments and produces a result.
* This is the three-arity specialization of {@link Function}.
*
* @param <T>
* the type of the first argument to the function
* @param <U>
* the type of the second argument to the function
* @param <V>
* the type of the third argument to the function
* @param <R>
* the type of the result of the function
*
* @see Function
*/
@FunctionalInterface
public interface TriFunction<T, U, V, R> {
R apply(T t, U u, V v);
}
接受多个参数的方法;你想提供其中的一些:
private static boolean manyArgs(String str, int i, double d, float f) {
return true;
}
以下是您如何使用自定义函数对象:
/*
* Pass one of the arguments. This creates a function accepting three
* arguments.
*/
TriFunction<Integer, Double, Float, Boolean> partiallyApplied = (i, d, f) ->
manyArgs("", i, d, f);
/*
* Provide the rest of the arguments.
*/
boolean res4 = partiallyApplied.apply(2, 3.0, 4.0F);
System.out.println("No time for ceremonies: " + res4);
关于java - Java 8 中的偏函数应用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22577261/