简化Java数组布局

Question

is there any other way of applying this table to array rather than creating 31 of them?

The layout looks like:

state_name|year|crimetype1|crimetype2|place|count|

---

row1: state1|2001|murder|knife|home|5|

row2: state1|2001|murder|axe|home|2|

row3: state2|2001|robbery|baseball|shop|1|

and so on for 31 different states.

I thought of creating 31 arrays for each state with 5 rows but is there any other way of making it simpler?

Answer 1

Simply put: objects. That way, you will not have to have nested arrays.

Make a class:

public class Crime{
    private int year;
    private String state;
    private String crimeType1, crimeType2;
    private String place;
    private int count;

    //And then you'd have some useful stuff here...
}

Besides this, I don't think you should combine the 31 values anymore - they are 31 separate, independent occurrences.

Answer 2

First, create a Crime object which can represent a single row in that collection. Let's make it naturally comparable against itself based on the state.

public class Crime implements Comparable<Crime> {
    private String state;
    private Year year;
    private String crimeType1;
    private String crimeType2;
    private String place;
    private int count;

    public int compareTo(Crime other) {
        return state.compareTo(other.state);
    }
}

I leave the construction of this object as an exercise for the reader.

Next, you'll want to add the results of that value to a list.

List<Crime> crimes = new ArrayList<>();

// In a loop reading the file
    crimes.add(crime);

At this point your work is pretty much done; if you want to get the crimes by a specific state, you can use the Stream API to filter based on that.

Answer 3

It is better to create class Crime as follows getHeader() returns header and getRow will return the row . (or toString)

public class Crime {

    String stateName;
    String year;
    //...

    public static String getHeader(){
        //you can improve this
        return "state_name|year|crimetype1|crimetype2|place|count|";
    }

    public String getRow(){        
        return stateName + "|" + year +"|" ...
    }

    public static void main(String[] args) {
        List<Crime> state  = new ArrayList<>(31);
        //or 
        List<Crime> state = Arrays.asList(new Crime[] {
           new Crime("ST","2004",..),... 
        });
    }
}

Answer 4

as KevinO pointed if you are coding OO language it is good to think in OO way otherwise there no point of using java .

Create a Crime class with all the values except state and then a Map

Map<String,ArrayList<Crime>> multiMap = new HashMap<String,ArrayList<Crime>>();

Here String is state name and the ArrayList for all the crimes in that state, So at the end there will be 31 keys (Here we are using state as unique keys) in muliMap Object .

So later you no need to filter statewise crimes, all you need to do is

ArrayList<Crime> state1Crimes = multiMap.get("state1");

Simple and straight forward.