下面有两个文件:
Egg.java
package doItMyself;public enum Egg {
// the enum constants, which "call" the constructor
jumbo(30.0),
extraLarge(27.0),
large(24.0);
Egg(double w){ //constructor
weight=w;
}
private double weight;
public double getWeight(){
return weight;
}
}BigEgg.java
package doItMyself;public class BigEgg {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Egg e=Egg.jumbo;
double wt=e.getWeight();
System.out.println(e+" eggs weight "+wt+" oz. per doz.");
}
}当运行BigEgg后,出现
Exception in thread "main" java.lang.NullPointerException at doItMyself.BigEgg.main(BigEgg.java:28),为什么?
Egg.java
package doItMyself;public enum Egg {
// the enum constants, which "call" the constructor
jumbo(30.0),
extraLarge(27.0),
large(24.0);
Egg(double w){ //constructor
weight=w;
}
private double weight;
public double getWeight(){
return weight;
}
}BigEgg.java
package doItMyself;public class BigEgg {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Egg e=Egg.jumbo;
double wt=e.getWeight();
System.out.println(e+" eggs weight "+wt+" oz. per doz.");
}
}当运行BigEgg后,出现
Exception in thread "main" java.lang.NullPointerException at doItMyself.BigEgg.main(BigEgg.java:28),为什么?
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final double a = 1;
final double b = 2;或者你就直接放个内部类进去
用final double这样没有强制性,我方法a(Egg e)则你很清楚方法的所需要的参数,而a(double e)这样你根本不可能马上知道这个e是什么意思
那我想问一下,
在实际应用中,enum在什么地方比较方便