Java- HashMap.get returns null 不应该的时候

Question

我正在使用 HashMap 将一些字符串 link 转换为整数，然后将其用于索引列表。我在 .get() 中使用的字符串从 android 微调器传递给方法，并且在我将它们输出到日志时绝对正确，并且它们与 HashMap 中的字符串匹配。但是，使用这些字符串之一调用 .get returns null，随后当我尝试在计算中使用 null 整数时导致应用程序强制关闭。

 HashMap<String, Integer> valuesOfAngleUnits = new HashMap<String, Integer>();

public void setValuesOfAngleUnits(HashMap<String, Integer> valuesOfAngleUnits) {
    valuesOfAngleUnits.put("Arc minute", 0);
    valuesOfAngleUnits.put("Arc second", 1);
    valuesOfAngleUnits.put("Degree", 2);
    valuesOfAngleUnits.put("Gon", 3);
    valuesOfAngleUnits.put("Grad", 4);
    valuesOfAngleUnits.put("Mil (Nato)", 5);
    valuesOfAngleUnits.put("Mil (Soviet Union)", 6);
    valuesOfAngleUnits.put("Octant", 7);
    valuesOfAngleUnits.put("Quadrant", 8);
    valuesOfAngleUnits.put("Radian", 9);
    valuesOfAngleUnits.put("Revolution", 10);
    valuesOfAngleUnits.put("Sextant", 11);
    valuesOfAngleUnits.put("Sign", 12);
    valuesOfAngleUnits.put("Turn", 13);
}

List<Double> convertToArcSeconds = new ArrayList(Arrays.asList(1, 0.1666667, 0.000046, 0.0166667, 0.18519, 0.18519, 0.296296, 0.277778, 0.291667, 0.00037, 0.000185, 0.000291, 0.000046, 0.000278, 0.000556, 0.000046));


public void calculateConversion(String inputSpinner, String outputSpinner, Float userInput){
    Float output = new Float(0.0);
    String Tag = "Input collected";
    Log.v(Tag, "The input data type is " + inputSpinner + ". The output data type is " + outputSpinner + ", and the user input is " + userInput);
    Integer numericalValueOfInputSpinner = valuesOfAngleUnits.get(inputSpinner);
    Log.v(Tag, "The numerical value of the spinner is " + numericalValueOfInputSpinner);
    Float ArcSecondValue = new Float(userInput * convertToArcSeconds.get(numericalValueOfInputSpinner));
    String Tag2 = "ArcSecondValueFound";
    Log.v(Tag2, "The arc second value is " + ArcSecondValue);

}

上面的代码设置了一个 hashmap 和一个列表，并向您展示了所使用的方法。

    06-22 21:23:34.113    3728-3728/? V/Input collected﹕ The input data type is Arc minute. The output data type is Arc minute, and the user input is 7645.0
06-22 21:23:34.113    3728-3728/? V/Input collected﹕ The numerical value of the spinner is null
06-22 21:23:34.113    3728-3728/? D/AndroidRuntime﹕ Shutting down VM
06-22 21:23:34.114    3728-3728/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.anapp.tpb.sidebarproject, PID: 3728
    java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Integer.intValue()' on a null object reference
            at com.anapp.tpb.sidebarproject.MainActivity.calculateConversion(MainActivity.java:78)
            at com.anapp.tpb.sidebarproject.MainActivity.onClick(MainActivity.java:100)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-22 21:23:34.114    1224-1388/? W/ActivityManager﹕ Force finishing activity 1 com.anapp.tpb.sidebarproject/.MainActivity

以上是 logcat 输出。前两行显示已将正确的字符串连同一个浮点数传递给该方法。但是，数值为空。我不明白为什么会这样，因为字符串 "Arc minute" 在 valuesOfAngleUnits HashMap 中。

感谢任何帮助。

Answer 1

这看起来像问题所在：

HashMap<String, Integer> valuesOfAngleUnits = new HashMap<String, Integer>();

public void setValuesOfAngleUnits(HashMap<String, Integer> valuesOfAngleUnits) {
    valuesOfAngleUnits.put("Arc minute", 0);
    valuesOfAngleUnits.put("Arc second", 1);
    valuesOfAngleUnits.put("Degree", 2);
    valuesOfAngleUnits.put("Gon", 3);
    valuesOfAngleUnits.put("Grad", 4);
    valuesOfAngleUnits.put("Mil (Nato)", 5);
    valuesOfAngleUnits.put("Mil (Soviet Union)", 6);
    valuesOfAngleUnits.put("Octant", 7);
    valuesOfAngleUnits.put("Quadrant", 8);
    valuesOfAngleUnits.put("Radian", 9);
    valuesOfAngleUnits.put("Revolution", 10);
    valuesOfAngleUnits.put("Sextant", 11);
    valuesOfAngleUnits.put("Sign", 12);
    valuesOfAngleUnits.put("Turn", 13);
}

您正在初始化传递给该方法的本地 HashMap，它可能与同名的实例变量不同。

改为：

public void setValuesOfAngleUnits() {
    valuesOfAngleUnits.put("Arc minute", 0);
    valuesOfAngleUnits.put("Arc second", 1);
    valuesOfAngleUnits.put("Degree", 2);
    valuesOfAngleUnits.put("Gon", 3);
    valuesOfAngleUnits.put("Grad", 4);
    valuesOfAngleUnits.put("Mil (Nato)", 5);
    valuesOfAngleUnits.put("Mil (Soviet Union)", 6);
    valuesOfAngleUnits.put("Octant", 7);
    valuesOfAngleUnits.put("Quadrant", 8);
    valuesOfAngleUnits.put("Radian", 9);
    valuesOfAngleUnits.put("Revolution", 10);
    valuesOfAngleUnits.put("Sextant", 11);
    valuesOfAngleUnits.put("Sign", 12);
    valuesOfAngleUnits.put("Turn", 13);
}

Java- HashMap.get returns null 不应该的时候

Java- HashMap.get returns null when it shouldn't

java

null

android

hashmap