Java 8函数式编程

Question

我正在寻找实现小通用函数，以执行树结构上的不同操作。在收集结果方面需要帮助。

示例：

public static <R> R collect(final Constraint root, Function<Constraint, R> function) {      
        if(root == null) { // return here }

        //apply function to current node and collect result here
        function.apply(root);

        // If has more children recurse.
        if(root.getConstraints() != null && !root.getConstraints().isEmpty()) {
            root.getConstraints().forEach(e -> collect(e, function));
        }
}

这可以用于以下情况：-收集没有子节点的所有节点-收集所有具有子节点的节点-收集满足某些特定条件的节点。

Answer 1

Map怎么样？

public static <R> Map<Constraint, R> collect(final Constraint root, Function<Constraint, R> function) {
    Map<Constraint, R> results = new HashMap<>();
    collect(root, function, results);
    return results;
}

private static <R> void collect(final Constraint root, Function<Constraint, R> function, Map<Constraint, R> results) {
    if (root != null) { // return here }

        //apply function to current node and collect result here
        results.put(root, function.apply(root));

        // If has more children recurse.
        if (root.getConstraints() != null && !root.getConstraints().isEmpty()) {
            root.getConstraints().forEach(e -> collect(e, function, results));
        }
    }
}