Java HashMaps为什么会返回null？

Question

I setup a test jar app to run for my other program I have been working on this for hours and i cant find a reason for why it returns null. Thanks for helping!

hashy.java

import java.util.HashMap;

public class hashy {

private static HashMap<String, Integer> targets = new HashMap<String, Integer>();

public static void main(String[] args) {
    Hashymashy mash = new Hashymashy();
    mash.hashyMash();
    String name = "Bobby";
    int num = 10;

    targets.put(name, num);

    if (targets.containsKey(name) == true) {
        System.out.println("It contains a key!");
    } else {
        System.out.println("It does not contain a key!");
    }
    if (targets.containsValue(num) == true) {
        System.out.println("It contains a value");
    } else {
        System.out.println("It does not contain a value!");
    }
}
public HashMap<String,Integer> getTargets(){
    return targets;
}
}

Hashymashy.java

 public class Hashymashy {

public void hashyMash(){
    hashy h = new hashy();
    String name = "Bobby";
    Integer fnum = h.getTargets().get(name);

    System.out.println("Number is "+fnum+"!");
}
}

Answer 1

You are trying to retrieve the value associated with "Bobby" before adding it to the HashMap .

mash.hashyMash();

is called before targets.put(name, num); , so

Integer fnum = h.getTargets().get("Bobby");

will return null since there is no "Bobby" yet .

PS : seems like a bad design to me, since Hashymashy classes create instances of hashy classes & vice-versa.