我非常熟悉在其他语言中使用枚举,但我在 Java 中遇到了一些特殊用途的困难。
Sun 的枚举文档大胆地指出:
"Java programming language enums are far more powerful than their counterparts in other languages, which are little more than glorified integers."
好吧,这很不错,但出于 switch 语句中比较的原因,我有点需要每个枚举都有一个常量数据类型表示。情况如下:我正在构建代表给定空间的节点,或迷宫图中的“插槽”,并且这些节点必须能够从代表迷宫的二维整数数组中构建。这是我为 MazeNode 类得到的,这是目前的问题所在(switch 语句咆哮):
注意:由于 case 语句中的动态项,我知道这段代码不起作用。它是为了说明我所追求的。
public class MazeNode
{
public enum SlotValue
{
empty(0),
start(1),
wall(2),
visited(3),
end(9);
private int m_representation;
SlotValue(int representation)
{
m_representation = representation;
}
public int getRepresentation()
{
return m_representation;
}
}
private SlotValue m_mazeNodeSlotValue;
public MazeNode(SlotValue s)
{
m_mazeNodeSlotValue = s;
}
public MazeNode(int s)
{
switch(s)
{
case SlotValue.empty.getRepresentation():
m_mazeNodeSlotValue = SlotValue.start;
break;
case SlotValue.end.getRepresentation():
m_mazeNodeSlotValue = SlotValue.end;
break;
}
}
public SlotValue getSlotValue()
{
return m_mazeNodeSlotValue;
}
}
所以代码在 switch 语句上提示“case 表达式必须是常量表达式”——我明白为什么编译器可能有问题,因为从技术上讲它们是动态的,但我不确定采用什么方法来解决这个。有没有更好的办法?
最重要的是,我需要枚举具有相应的整数值,以便与程序中传入的二维整数数组进行比较。
最佳答案
你可以这样使用:
import java.util.HashMap;
import java.util.Map;
public class MazeNode {
public enum SlotValue {
empty(0), start(1), wall(2), visited(3), end(9);
protected int m_representation;
SlotValue(int representation) {
m_representation = representation;
}
private static final Map<Integer, SlotValue> mapping = new HashMap<Integer, SlotValue>();
static {
for (SlotValue slotValue : SlotValue.values()) {
mapping.put(slotValue.m_representation, slotValue);
}
}
public static SlotValue fromRepresentation(int representation) {
SlotValue slotValue = SlotValue.mapping.get(representation);
if (slotValue == null)
// throw your own exception
throw new RuntimeException("Invalid representation:" + representation);
return slotValue;
}
}
private SlotValue m_mazeNodeSlotValue;
public MazeNode(SlotValue s) {
m_mazeNodeSlotValue = s;
}
public MazeNode(int s) {
m_mazeNodeSlotValue = SlotValue.fromRepresentation(s);
}
public SlotValue getSlotValue() {
return m_mazeNodeSlotValue;
}
public static void main(String[] args) {
MazeNode m = new MazeNode(2);
System.out.println(m.getSlotValue());
m = new MazeNode(9);
System.out.println(m.getSlotValue());
}
}
关于java - Java 中枚举值表示的 Switch 语句,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1052244/