Question

我有一个ArrayList<Item>，如下所示

        ArrayList<Item> items = new ArrayList<Item>();
        items.add(new SectionItem("Category 1"));
        items.add(new EntryItem("Item 1", "This is item 1.1"));
        items.add(new EntryItem("Item 2", "This is item 1.2"));
        items.add(new EntryItem("Item 3", "This is item 1.3"));


        items.add(new SectionItem("Category 2"));
        items.add(new EntryItem("Item 4", "This is item 2.1"));
        items.add(new EntryItem("Item 5", "This is item 2.2"));
        items.add(new EntryItem("Item 6", "This is item 2.3"));
        items.add(new EntryItem("Item 7", "This is item 2.4"));

        items.add(new SectionItem("Category 3"));
        items.add(new EntryItem("Item 8", "This is item 3.1"));
        items.add(new EntryItem("Item 9", "This is item 3.2"));
        items.add(new EntryItem("Item 10", "This is item 3.3"));
        items.add(new EntryItem("Item 11", "This is item 3.4"));
        items.add(new EntryItem("Item 12", "This is item 3.5"));

我想将其转换为List<String>。我怎样才能做到这一点？我做了如下，但它没有工作。

        List<String> result = new ArrayList<String>();
        for (Object Item : items) {
            result.add(Item != null ? Item.toString() : null);
        }

下面是我的sectionItem和EntryItem

public class SectionItem implements Item{

    private final String title;

    public SectionItem(String title) {
        this.title = title;
    }

    public String getTitle(){
        return title;
    }

    @Override
    public boolean isSection() {
        return true;
    }
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return super.toString();
    }

}

public class EntryItem implements Item{

    public final String title;
    public final String subtitle;

    public EntryItem(String title, String subtitle) {
        this.title = title;
        this.subtitle = subtitle;
    }

    @Override
    public boolean isSection() {
        return false;
    }
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return super.toString();
    }

}

Answer 1

以下是字符串示例。

    List<String> itemsList2 = new ArrayList<String>(items);
    for(String item:itemsList2)
        System.out.println(item);

如果要分配新内存，并创建arraylist副本。

    List<String> itemsList= items;
    for(String item:itemsList)
        System.out.println(item);

如果您只想将其映射到列表，并重复使用相同的arraylist对象。

{{1}}

Answer 2

您应该使用if而不是尝试将null添加到列表中：

List<String> result = new ArrayList<String>();
        for (Object Item : items) {
            if(Item != null)
                result.add(Item.toString());

Java将ArrayList <object>转换为List <string>

2 个答案: