Question

创建一个双精度数组（用于状态的一行，用于国会大厦的一行），我试图在for循环中使用“ map.put”来保存数组“键（状态）”和“值（国会大厦）”到HashMap。在分配新的HashMap（hMap = getInfo（）;之后，使用来自用户输入的键时，我的输出返回“ null”。我不太确定自己在做什么错，但是我有种感觉，我为循环

public class HashMapProgram {

    public static void main (String[]args) {

        Scanner input = new Scanner(System.in);

        //Assign contents of map in getInfo to hMap
        HashMap<String, String> hMap = getInfo();


        //Prompting user to input a state (key)
            System.out.print("Enter a state, or \"done\" when finished: ");
            String state = input.next();



        if(hMap.get(state) != "done")
                System.out.println("The capital is "+ hMap.get(state));


    }


    public static HashMap<String, String> getInfo(){

        //HashMap to save contents in
        HashMap<String, String> map = new HashMap<>();

        String x[][] = {
                {"Alabama","Alaska","Arizona"  ,"Arkansas","California","Colorado","Connecticut","Delaware","Florida","Georgia",
                "Hawaii"  ,"Idaho" ,"Illinois" ,"Indiana" ,"Iowa","Kansas","Kentucky","Louisiana","Maine","Maryland",
                "Massachusetts","Michigan","Minnesota","Mississippi","Missouri","Montana","Nebraska","Nevada","New Hampshire","New Jersey",
                "New Mexico","New York","North Carolina","North Dakota","Ohio","Oklahoma","Oregon","Pennsylvania",  "Rhode Island", "South Carolina",
                "South Dakota", "Tennessee",    "Texas",    "Utah", "Vermont",  "Virginia", "Washington","West Virginia","Wisconsin","Wyoming"},

                {"Montgomery","Juneau","Phoenix","Little Rock","Sacramento","Denver","Hartford","Dover","Tallahassee","Atlanta",
                "Honolulu","Boise","Springfield","Indianapolis","Des Moines","Topeka","Frankfort","Baton Rouge","Augusta", "Annapolis",
                "Boston","Lansing","St. Paul","Jackson","Jefferson City","Helena","Lincoln","Carson City","Concord","Trenton",
                "Santa Fe","Albany","Raleigh","Bismarck","Columbus","Oklahoma City","Salem","Harrisburg","Providence","Columbia",
                "Pierre","Nashville","Austin","Salt Lake City","Montpelier","Richmond","Olympia","Charleston","Madison","Cheyenne"}

        };



        //Saving contents in 'map'
        for(int i = 0; i < x.length; i++) {     
            map.put(x[0][i], x[1][i]);  
        }

        return map;
    }
}

Answer 1

有一些错误：

1）在for循环中，将i < x.length;更改为i < x[0].length;，否则您将仅运行2次循环。

2）不要使用!=比较字符串。请改用equals()。有关更多详细信息，请参见this。

3）您没有循环可重复要求用户输入。将main()中的代码更改为：

Scanner input = new Scanner(System.in);
HashMap<String, String> hMap = getInfo();
String state = "";
do {
    System.out.print("Enter a state, or \"done\" when finished: ");
    state = input.next();
    System.out.println("The capital is " + hMap.get(state));
} while (!state.equals("done"));

4）使用界面而非类。因此，更改

HashMap<String, String> hMap = getInfo();

到

Map<String, String> hMap = getInfo();

并更新方法签名以返回Map<String, String>。

5）从Java 9开始，您可以像这样直接创建地图：

Map<String, String> m = Map.of(
        "Alabama", "Montgomery",
        "Alaska", "Juneau",
        "Arizona", "Phoenix"
        //and so on...
);

将数据从双数组传输到HashMap

1 个答案: