Question

我正在尝试使用removeAll对ArrayList进行减法操作。但结果并不像预期的那样。实际上它没有删除任何东西。

ArrayList<Integer> tempSelectedPrivilges = new ArrayList<Integer>(privPickList.getTarget());
log.debug("Original selected : " + selectedPrivilges);        
log.debug("temp selected : " + tempSelectedPrivilges);
ArrayList<Integer> addedPrivileges = new ArrayList<>(tempSelectedPrivilges);
ArrayList<Integer> deletedPrivileges = new ArrayList<>(selectedPrivilges);        
log.debug("Add : " + addedPrivileges);
log.debug("Delete : " + deletedPrivileges);
addedPrivileges.removeAll(selectedPrivilges);
deletedPrivileges.removeAll(tempSelectedPrivilges);
log.debug("Add : " + addedPrivileges);
log.debug("Delete : " + deletedPrivileges);

输出是这样的：

Original selected : [2, 3]
temp selected : [2, 1, 4, 5, 6]
Add : [2, 1, 4, 5, 6]
Delete : [2, 3]
Add : [2, 1, 4, 5, 6]
Delete : [2, 3]

我看到的唯一问题是：

 privPickList.getTarget() returns a List<Integer> rather than ArrayList<Integer>.

因为当我创建像这样的tempSelectedPrivileges时，它的工作完全正常：

ArrayList<Integer> tempSelectedPrivilges = new ArrayList<>();
tempSelectedPrivilges.add(3);
tempSelectedPrivilges.add(5);
tempSelectedPrivilges.add(6);

为什么从整数列表创建整数ArayList会产生问题？

当我想要做的时候：

for(Integer i : privPickList.getTarget()) {
    tempSelectedPrivilges.add(i);
}

没有编译时错误。但运行时错误

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer

在线

tempSelectedPrivilges.add(i);

Answer 1

适用于我（使用List<Integer>）在Java 8中正常工作，

public static void main(String[] args) throws Exception {
    List<Integer> selectedPrivilges = new ArrayList<>(Arrays.asList(2, 3));
    List<Integer> tempSelectedPrivilges = new ArrayList<>(Arrays.asList(2,
            1, 4, 5, 6));
    System.out.println("Original selected : " + selectedPrivilges);
    System.out.println("temp selected : " + tempSelectedPrivilges);
    List<Integer> addedPrivileges = new ArrayList<>(tempSelectedPrivilges);
    List<Integer> deletedPrivileges = new ArrayList<>(selectedPrivilges);
    System.out.println("Add : " + addedPrivileges);
    System.out.println("Delete : " + deletedPrivileges);
    addedPrivileges.removeAll(selectedPrivilges);
    deletedPrivileges.removeAll(tempSelectedPrivilges);
    System.out.println("Add : " + addedPrivileges);
    System.out.println("Delete : " + deletedPrivileges);
}

输出（正如您所期望的那样）

Original selected : [2, 3]
temp selected : [2, 1, 4, 5, 6]
Add : [2, 1, 4, 5, 6]
Delete : [2, 3]
Add : [1, 4, 5, 6]
Delete : [3]

在ArrayList <integer>中的removeAll操作不能按预期工作</integer>

1 个答案: