Question

我正在尝试回答this question about parsing data and sorting into bins。我想我几乎已经解决了，但似乎无法让它正常工作。

这是我的代码：

package soBins;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Bins {

    public static void main(String[] args) {

        String rangeIn = "100 101 3.45\n101 102 4.23\n103 104 2.40\n199 200 6.89";

        String dataIn = "xx 108.45\nxx 122.00\nyy 124.78\nxx 156.93\nzz 101.5\nxx 103.5\nzz 101.25";

        Scanner rangeScanner = new Scanner(rangeIn);
        Scanner dataScanner = new Scanner(dataIn);  

        ArrayList<Bin> bins = new ArrayList<Bin>();
        while (rangeScanner.hasNextLine()) {
            String line = rangeScanner.nextLine();
            String[] tokens = line.split(" ");
            int min = Integer.parseInt(tokens[0]);
            int max = Integer.parseInt(tokens[1]);
//          System.out.println("Creating new bin, min "+ min + ", max "+ max);
            bins.add(new Bin(min,max));
        }

        Map<String,ArrayList<Bin>> namedBins = new HashMap<String,ArrayList<Bin>>();
        while (dataScanner.hasNextLine()) {
            String line = dataScanner.nextLine();
            String[] tokens = line.split(" ");
            String name = tokens[0]; // name is first token on line
            float data = Float.parseFloat(tokens[1]); // data is second token on line

            if (!namedBins.containsKey(name)) {
                // Shouldn't this create a new copy of the ArrayList of bins??
                namedBins.put(name, new ArrayList<Bin>(bins));
            }
            for (Bin b : namedBins.get(name)) {
                if (b.isInRange(data)) {
                    System.out.println("adding "+ data + " to bin in "+ name);
                    b.addData(data);

                }
            }
        }   

        System.out.println("All bins and data contents:");
        for (String dataName : namedBins.keySet()) { // print all values and bin ranges
            for (Bin range : namedBins.get(dataName)) {
                System.out.println(dataName + ", min " + range.getMin() + ", max " + range.getMax()
                        + ", data is " + range.getData());              
            }
        }
    }
}

我的Bin课程：

package soBins;

import java.util.ArrayList;

public class Bin {

    int min = 0;
    int max = 0;
    ArrayList<Float> values = new ArrayList<Float>();

    Bin(int min,int max) {
        this.min = min;
        this.max = max;
    }

    public boolean isInRange(float data) {
        return (min < data) && (data < max);
    }

    public void addData(float data) {
        values.add(data);
    }

    public int getMin() {
        return min;
    }
    public void setMin(int min) {
        this.min = min;
    }
    public int getMax() {
        return max;
    }
    public void setMax(int max) {
        this.max = max;
    }

    public ArrayList<Float> getData() {
        return values;
    }   

}

输出似乎是将数据添加到每个数据集，而不仅仅是它的意图。

输出结果为：

adding 101.5 to bin in zz
adding 103.5 to bin in xx
adding 101.25 to bin in zz
All bins and data contents:
zz, min 100, max 101, data is []
zz, min 101, max 102, data is [101.5, 101.25]
zz, min 103, max 104, data is [103.5]
zz, min 199, max 200, data is []
yy, min 100, max 101, data is []
yy, min 101, max 102, data is [101.5, 101.25]
yy, min 103, max 104, data is [103.5]
yy, min 199, max 200, data is []
xx, min 100, max 101, data is []
xx, min 101, max 102, data is [101.5, 101.25]
xx, min 103, max 104, data is [103.5]
xx, min 199, max 200, data is []

为什么它会添加到所有组中，而不仅仅是添加到目标组？

Answer 1

您只需创建一次Bin个实例，并在初始化地图之前将其放入bins列表中：

ArrayList<Bin> bins = new ArrayList<Bin>();
while (rangeScanner.hasNextLine()) {
    ....
    bins.add(new Bin(min,max));
}

并使用相同的bins实例初始化Map的所有键的值：

namedBins.put(name, new ArrayList<Bin>(bins));

虽然此语句为每个ArrayList条目创建一个新的Map，但它会从原始Bin列表中添加相同的bins个实例。这意味着Map中每个Bin列表中的Bin个实例都是相同的，因此当您修改这些Bin个实例时，您将更改所有Map条目。

为了在每个Bin条目中拥有唯一的Map个实例，您必须在Bin类中拥有复制构造函数或克隆方法。然后你会做这样的事情：

if (!namedBins.containsKey(name)) {
    List<Bin> newBins = new ArrayList<Bin>();
    newdBins.put(name, new newBins);
    for (Bin bin : bins)
        newBins.add (new Bin(bin)); // using a copy constructor            
}

如何定位列表地图中的条目？

1 个答案: