返回的 hashmap 值为 null

发布于 2024-12-06 23:25:24 字数 525 浏览 0 评论 0原文

我将自己限制在问题中我出错的部分。我有一个双精度值数组;我将数组中所有非零值放入哈希映射中,但是当我尝试在哈希映射中显示值时,我得到空值。 需要帮助。我无法弄清楚这是否与 Java 集合有关。

Map 是在 for 循环之外创建的。

for(int i=0;i<aray.length;i++) {
    if(aray[i]!=0) {
        //non zero array values get divided by some random number not too big number.  
        aray[i]=aray[i]/somenumber;
        hashmap.put(i,aray[i]); 
        System.out.println(hashmap.get(i));

        //if I display aray[i] its a non zero number but hashmap.get(i) is returning null values.  
    }
}

I am restricting myself to just to the part of the question where I am going wrong. I have an array of double values; I put all the values of the array which are non zero into the hash map but when I am trying to display the values in my hashmap I get null values.
Help needed.I have not been able to figure out if this has got something to with Java Collections.

The Map is created outside the for loop.

for(int i=0;i<aray.length;i++) {
    if(aray[i]!=0) {
        //non zero array values get divided by some random number not too big number.  
        aray[i]=aray[i]/somenumber;
        hashmap.put(i,aray[i]); 
        System.out.println(hashmap.get(i));

        //if I display aray[i] its a non zero number but hashmap.get(i) is returning null values.  
    }
}

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评论(1

谎言 2024-12-13 23:25:24

对我有用。

程序

class Test
{
    public static void main(String ... args)
    {
        final Integer somenumber = 2;
        final Integer[] aray = {5, 4, 3, 2, 1, 0, -1, -2, 42,};
        final java.util.HashMap<Integer, Integer> hashmap = new java.util.HashMap<Integer, Integer>();

        for(Integer i=0;i<aray.length;i++) {
            if(aray[i]!=0) {
                //non zero array values get divided by some random number not too big number.  
                aray[i]=aray[i]/somenumber;
                hashmap.put(i,aray[i]); 
                System.out.println(hashmap.get(i));
                //if I display aray[i] its a non zero number but hashmap.get(i) is returning null values.  
            }
        }
    }
}

输出

user@host:/tmp$ javac -version
javac 1.6.0_20
user@host:/tmp$ javac Test.java 
user@host:/tmp$ java Test 
2
2
1
1
0
0
-1
21

正如预期的那样,任何地方都没有空值。我看不出地图会返回空值,因为您刚刚添加了该值。

Works for me.

Program

class Test
{
    public static void main(String ... args)
    {
        final Integer somenumber = 2;
        final Integer[] aray = {5, 4, 3, 2, 1, 0, -1, -2, 42,};
        final java.util.HashMap<Integer, Integer> hashmap = new java.util.HashMap<Integer, Integer>();

        for(Integer i=0;i<aray.length;i++) {
            if(aray[i]!=0) {
                //non zero array values get divided by some random number not too big number.  
                aray[i]=aray[i]/somenumber;
                hashmap.put(i,aray[i]); 
                System.out.println(hashmap.get(i));
                //if I display aray[i] its a non zero number but hashmap.get(i) is returning null values.  
            }
        }
    }
}

Output

user@host:/tmp$ javac -version
javac 1.6.0_20
user@host:/tmp$ javac Test.java 
user@host:/tmp$ java Test 
2
2
1
1
0
0
-1
21

No null values anywhere, as expected. I don't see any way the map would be returning nulls, since you've just added the value.

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