ArrayListのメソッド

導入済み

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語彙

English	意味
ArrayList/əˈreɪ lɪst/	ArrayList

English

Replacement and removal return different results

set(i, x) replaces an existing element and returns the old value without changing size. remove(int i) removes the element at that position, returns it, and decreases size by one.
The overloaded remove(Object value) instead removes the first equal value and returns whether a match was removed. In an ArrayList<Integer>, remove(1) means index 1; use remove(Integer.valueOf(1)) to remove the value 1.

Example

import java.util.ArrayList;
import java.util.Arrays;

public class RemoveChoice {
    public static void main(String[] args) {
        ArrayList<Integer> byIndex = new ArrayList<>(Arrays.asList(1, 2, 1));
        ArrayList<Integer> byValue = new ArrayList<>(Arrays.asList(1, 2, 1));
        int removed = byIndex.remove(1);
        boolean found = byValue.remove(Integer.valueOf(1));
        System.out.println(removed + " " + byIndex);
        System.out.println(found + " " + byValue);
    }
}

The two outputs are 2 [1, 1] and true [2, 1]. Each list loses one element, but a different one.

Removing index 1 differs from removing Integer value 1

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