java - 如何在List/ArrayList中查找出现的位置

Question

我有一个关于如何查找列表中出现次数的问题。就我而言，对于我的程序的一部分，我试图查找飓风类别中 1、2、3 和 4 的出现次数并显示它们。我尝试使用 for 循环和 if 语句，但是当我运行它时，输出为零。我怎样才能解决这个问题？任何帮助将不胜感激。下面是我的程序的片段:

飓风2.java:

// category 1 occurrence
     int i = 0;
     int ii = 0;
     int category1 = category.get(i);
     for(int j = 0; j < category.size(); j++){
         if(category1 == 1){
             ii++;
         }
     }
System.out.printf("%1s%10d%n", "Category 1 occurrence ~", ii);

运行时我得到这个:

run:
                        Hurricanes 1980 - 2006

Year           Hurricane            Category        Pressure(mb)    Wind Speed (mph)
____________________________________________________________________________________
1980               Allen                   2                 100                 945
1983              Alicia                   2                 100                 962
1984               Diana                   2                 100                 949
1985                 Bob                   1                  65                1002
1985               Danny                   1                  80                 987
1985               Elena                   2                 100                 959
1985              Gloria                   1                  90                 942
1985                Juan                   1                  75                 971
1985                Kate                   1                  85                 967
1986              Bonnie                   1                  75                 990
1986             Charley                   1                  65                 990
1987               Floyd                   1                  65                 993
1988            Florence                   1                  70                 984
1989             Chantal                   1                  70                 986
1989                Hugo                   3                 120                 934
1989               Jerry                   1                  75                 983
1991                 Bob                   1                  90                 962
1992              Andrew                   4                 145                 922
1993               Emily                   2                 100                 960
1995                Erin                   1                  85                 973
1995                Opal                   2                 100                 942
1996              Bertha                   1                  90                 974
1996                Fran                   2                 100                 954
1997               Danny                   1                  70                 984
1998              Bonnie                   1                  95                 964
1998                Earl                   1                  70                 987
1998             Georges                   1                  90                 964
1999                Bret                   2                 100                 951
1999               Floyd                   1                  90                 956
1999               Irene                   1                  70                 987
2002                Lili                   1                  80                 963
2003           Claudette                   1                  80                 979
2003              Isabel                   1                  90                 957
2004                Alex                   1                  70                 972
2004             Charley                   4                 130                 941
2004              Gaston                   1                  65                 985
2004             Frances                   1                  90                 960
2004                Ivan                   2                 105                 946
2004              Jeanne                   2                 105                 950
2005               Cindy                   1                  65                 992
2005              Dennis                   4                 130                 930
2005               Emily                   4                 135                 929
2005               Irene                   1                  85                 975
2005             Katrina                   4                 150                 902
2005               Maria                   2                 100                 960
2005                Nate                   1                  80                 979
2005             Ophelia                   1                  80                 976
2005            Phillipe                   1                  70                 985
2005                Rita                   4                 150                 897
2005                Stan                   1                  70                 979
2005               Vince                   1                  65                 987
2005               Wilma                   4                 150                 882
2005                Beta                   2                 100                 960
2005             Epsilon                   1                  75                 979
2006             Ernesto                   1                  65                 995
2006            Florence                   1                  80                 972
2006              Gordon                   2                 105                 955
2006              Helene                   2                 110                 954
2006               Isaac                   1                  75                 985
____________________________________________________________________________________
Average ~                                  1                  91                 963
Maximum ~                                  4                 150                1002
Minimum ~                                  1                  65                 882
Category 1 occurrence ~         0
BUILD SUCCESSFUL (total time: 0 seconds)

Answer 1

使用 int[] 作为计数器，如下所示:

// we won't use the 0 position
int[] counter = new int[5];

迭代所有类别。每次找到新类别时，请向计数器添加一个:

for (int i = 0; i < category.size(); i++) {
    int cat = category.get(i);
    // assuming that cat is 1, 2, 3 or 4
    counter[cat]++;
}

当迭代结束时，counter[1]将保存第一个类别的出现次数，counter[2]将保存第二个类别的出现次数类别等。