Question

我想使用Java 8新引入的函数对象将一些参数部分应用于遗留方法。

以下是有问题的方法：

/**
 * 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;
}

Answer 1

这实现了我想要做的事情：

/*
 * Apply two arguments. The created function accepts a String and
 * returns a StringBuilder
 */
Function<String, StringBuilder> addEllipsis = appendToMe -> appendChar(
        '.', 3, appendToMe);
/*
 * Apply 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 applying 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");

有关函数对象的所有Java预定义变体的列表，请查看here。

修改

如果你有一个包含大量参数的方法，你可以编写自己的函数：

/** * 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); }

接受许多参数的方法;你想提供一些：

private static boolean manyArgs(String str, int i, double d, float f) { return true; }

以下是使用自定义函数对象的方法：

/* * 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);

Java 8中的部分函数应用程序

1 个答案: