视图对象的常量返回类型

import java.util.Collections;
import java.util.List;

public class ViewExample {
    private final List<String> data = Collections.singletonList("example");

    public List<String> getData() {
        return Collections.unmodifiableList(data);
    }

    public static void main(String[] args) {
        ViewExample example = new ViewExample();
        List<String> data = example.getData();
        // 下面的代码会抛出UnsupportedOperationException
        // data.add("new item");
    }
}

public class ViewExample {
    private List<String> data = new ArrayList<>();

    public List<String> getData() {
        return Collections.unmodifiableList(data);
    }

    public void addData(String item) {
        data.add(item);
    }
}