我如何成功地遍历一个预填充的ArrayList以找到每个连续元素的差异并将其打印出来？

Question

public class AccumulatedData {

    public static void main(String args[]) {

        ArrayList<Double> weights = new ArrayList<Double>();

        weights.add(145.0);
        weights.add(146.5);
        weights.add(146.5);
        weights.add(147.0);
        weights.add(146.0);
        weights.add(148.0);
        weights.add(148.5);

        ArrayList<Double> printWeightChanges = getWeightChanges(weights);
        System.out.println(weights);
    }

    public static ArrayList<Double> getWeightChanges(ArrayList<Double> weights) {

        for (int i = 0; i < weights.size() - 1; i++) {
            weights.set(i, (weights.get(i + 1) - weights.get(i)));
        }

        return weights;
    }

}

上面我尝试遍历数组列表的所有元素，并打印出它们各自的连续差值（取数组列表的索引1，减去索引零）。但是，我的for循环似乎遍历所有元素，打印它们各自的差值，然后将初始数组的最后一个数与所有差值一起添加到新数组列表的末尾。我怎么解决这个？

ublic类PartA{

public static void main(String args[]) {


    ArrayList<Double> weights = new ArrayList<Double>();


    weights.add(145.0);
    weights.add(146.5);
    weights.add(146.5);
    weights.add(147.0);
    weights.add(146.0);
    weights.add(148.0);
    weights.add(148.5);


    ArrayList<Double> printWeightChanges = getWeightChanges(weights);

新尝试：

}

/**
 * Part a
 */

public static ArrayList<Double> getWeightChanges(ArrayList<Double> weights) {

    ArrayList<Double> weightDifferences = new ArrayList <Double>();

    for (int i = 0; i < weights.size() - 1; i++) {
        weightDifferences.add(i, weights.get(i + 1) - weights.get(i));

    }

    System.out.println(weightDifferences);
    return weightDifferences;


    }

}

这会产生各种错误：

线程“main”java.lang.IndexOutoFboundsException：索引145超出长度6的界限，位于java.base/jdk.internal.util.preconditions.OutoFbounds(preconditions.java:64)位于java.base/jdk.internal.util.preconditions.OutoFboundscheckindex(preconditions.java:70)位于java.base/jdk.internal.util.preconditions.CheckIndex(preconditions.java:248)位于

从我的尝试中输出的我的尝试代码

Answer 1

这是因为您定义循环限制的方式：

for (int i = 0; i < weights.size() - 1; i++)

该循环比数组中的元素(i )少更改一个元素。

我建议为差异创建另一个列表，如下所示：

public static List<Double> getWeightChanges(ArrayList<Double> weights) {

    List<Double> diffs = new ArrayList<>();
    for (int i = 0; i < weights.size() - 1; i++) {
        diffs.add(weights.get(i + 1) - weights.get(i));
    }

    return diffs;
}