Question

我正试图替换com.google.common.graph.MutableValueGraph中的元素。

我需要在以下数据类上更新元素状态（我知道the docs建议小心）：

data class Frame(val method: String, val merged: Boolean = false)

由于图表没有提供一种方法来交换另一个节点，我自己动手：

fun MutableValueGraph<Frame, Int>.exchangeNode(old: Frame, new: Frame): Boolean {
    if (old == new) return true

    if (isDirected) {
        this.predecessors(old).forEach { 
            this.putEdgeValue(it, new, this.edgeValue(it, old)) }
        this.successors(old).forEach { 
            this.putEdgeValue(new, it, this.edgeValue(old, it)) }
    } else {
        this.adjacentNodes(old).forEach { 
            this.putEdgeValue(it, new, this.edgeValue(it, old)) }
    }
    return this.removeNode(old)
}

但是，我遇到了ConcurrentModificationException：

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1437)
at java.util.HashMap$EntryIterator.next(HashMap.java:1471)
at java.util.HashMap$EntryIterator.next(HashMap.java:1469)
at com.google.common.graph.DirectedGraphConnections$1$1.computeNext(DirectedGraphConnections.java:113)
at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:145)
at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:140)
at TestKt.exchangeNode(Test.kt:292)
...

听起来很公平，因为我在for循环中交换了一堆节点，可能试图触摸已经交换过的相邻节点？

我的问题是：如何替换ValueGraph中的多个节点，保持其边缘值？

Answer 1

一种效率较低的方法，但应该避免ConcurrentModificationException的方法是从相关节点引出子图，然后删除旧节点并添加新节点，最后使用诱导子图将边值重新添加到：

fun MutableValueGraph<Frame, Int>.exchangeNode(old: Frame, new: Frame): Boolean {
    if (old == new) return false

    val inducedSubgraph = Graphs.inducedSubgraph(this, adjacentNodes(old) + old)

    removeNode(old)
    addNode(new)

    if (isDirected) {
        for (predecessor in inducedSubgraph.predecessors(old)) {
            putEdgeValue(predecessor, new, inducedSubgraph.edgeValue(predecessor, old))
        }
        for (successor in inducedSubgraph.successors(old)) {
            putEdgeValue(new, successor, inducedSubgraph.edgeValue(old, successor))
        }
    } else {
        for (adjacentNode in inducedSubgraph.adjacentNodes(old)) {
            putEdgeValue(adjacentNode, new, inducedSubgraph.edgeValue(adjacentNode, old))
        }
    }

    return true
}

在Guava MutableValueGraph中交换节点

1 个答案: