枚举
public enum PlayerType {
TENNIS,
FOOTBALL,
BASKETBALL
}
Java 编译器帮我们做了很多隐式的工作,看一下反编译后的字节码:
public final class PlayerType extends Enum
{
public static PlayerType[] values()
{
return (PlayerType[])$VALUES.clone();
}
public static PlayerType valueOf(String name)
{
return (PlayerType)Enum.valueOf(com/cmower/baeldung/enum1/PlayerType, name);
}
private PlayerType(String s, int i)
{
super(s, i);
}
public static final PlayerType TENNIS;
public static final PlayerType FOOTBALL;
public static final PlayerType BASKETBALL;
private static final PlayerType $VALUES[];
static
{
TENNIS = new PlayerType("TENNIS", 0);
FOOTBALL = new PlayerType("FOOTBALL", 1);
BASKETBALL = new PlayerType("BASKETBALL", 2);
$VALUES = (new PlayerType[] {
TENNIS, FOOTBALL, BASKETBALL
});
}
}
要继承 Enum 类;
要写构造方法;
要声明静态变量和数组;
要用 static 块来初始化静态变量和数组;
要提供静态方法,比如说
values()
和valueOf(String name)
枚举是一种特殊的类,那它其实是可以定义在一个类的内部的,这样它的作用域就可以限定于这个外部类中使用。
public class Player {
private PlayerType type;
public enum PlayerType {
TENNIS,
FOOTBALL,
BASKETBALL
}
public boolean isBasketballPlayer() {
return getType() == PlayerType.BASKETBALL;
}
public PlayerType getType() {
return type;
}
public void setType(PlayerType type) {
this.type = type;
}
}
参照 isBasketballPlayer()
方法,由于枚举是 final 的,所以可以确保在 Java 虚拟机中仅有一个常量对象,基于这个原因,我们可以使用“==”运算符来比较两个枚举是否相等。
如果枚举中需要包含更多信息的话,可以为其添加一些字段:
public enum PlayerType {
TENNIS("网球"),
FOOTBALL("足球"),
BASKETBALL("篮球");
private String name;
PlayerType(String name) {
this.name = name;
}
}
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