无法从Enumeration<TreeNode>转换为Enumeration<DefaultMutableTreeNode>

Question

在执行任务时，我遇到了"Legacy code"，它是用Java8编译的，但不是用Java16编译的，它使用的是这段特定的代码。

protected void onCalculate() {
    final ConsoleMapperForTree cm = new ConsoleMapperForTree();
    cm.setVisible(true);
    cm.getConsole().setFont(new Font("Tahoma", 0, 20));
    final DefaultMutableTreeNode root = (DefaultMutableTreeNode)this.tree.getModel().getRoot();
    final Enumeration<DefaultMutableTreeNode> enmFclt = (Enumeration<DefaultMutableTreeNode>)root.children(); // this is highlighted as an error
    while (enmFclt.hasMoreElements()) {
        final DefaultMutableTreeNode fclt = enmFclt.nextElement();
        int nSpec = 0;
        final Enumeration<DefaultMutableTreeNode> enmDep = (Enumeration<DefaultMutableTreeNode>)fclt.children(); // this is highlighted as an error
        while (enmDep.hasMoreElements()) {
            final DefaultMutableTreeNode dep = enmDep.nextElement();
            final Object data = dep.getUserObject();
            if (((Dept)data).spec) {
                ++nSpec;
            }
        }
        System.out.println(fclt + " has " + nSpec + " specdepartments");
    }
}

Answer 1

问题是Java希望您对树的元素执行类型转换，而不是对整个树执行类型转换。因此，请尝试按如下方式移动类型转换运算符：

protected void onCalculate() {
    final ConsoleMapperForTree cm = new ConsoleMapperForTree();
    cm.setVisible(true);
    cm.getConsole().setFont(new Font("Tahoma", 0, 20));
    final DefaultMutableTreeNode root = (DefaultMutableTreeNode)this.tree.getModel().getRoot();
    final Enumeration<TreeNode> enmFclt = root.children(); // this is highlighted as an error
    while (enmFclt.hasMoreElements()) {
        final DefaultMutableTreeNode fclt = (DefaultMutableTreeNode) enmFclt.nextElement();
        int nSpec = 0;
        final Enumeration<TreeNode> enmDep = fclt.children(); // this is highlighted as an error
        while (enmDep.hasMoreElements()) {
            final DefaultMutableTreeNode dep = (DefaultMutableTreeNode) enmDep.nextElement();
            final Object data = dep.getUserObject();
            if (((Dept)data).spec) {
                ++nSpec;
            }
        }
        System.out.println(fclt + " has " + nSpec + " specdepartments");
    }
}

这种并列比较显示了不同之处(单击可放大)：

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