java - ArrayList 并返回 null

Question

我正在尝试完成我的方法“优先级”，该方法应返回任务的优先级。如果指定的名称不存在(如 main 所示)，则使其返回 null 。我尝试过遍历 ArrayList，但我不认为这是这样做的方法。有谁可以帮帮我吗？

class Task
{
    public static final ArrayList<Task> ALL_TASKS = new ArrayList<>();

    private String name;
    private Integer priority;

    public Task(String name, Integer priority)
    {
        this.name = name;
        this.priority = priority;
        ALL_TASKS.add(this);
    }

    @Override public String toString()
    {
        return "name: " + this.name + "\tpriority: " + this.priority;
    }
}

class Main
{
    public static void main(String[] arguments)
    {
        new Task("Clean", 5);
        new Task("Dishwash", 4);
        new Task("Study", 1);
        System.out.println(Task.priority("Dishwash"));
        System.out.println(Task.priority("Vacuumclean"));
    }
}

Answer 1

试试这个:

public static Integer priority(String name) {
    for(Task task : ALL_TASKS) {
        if(task.name.equals(name)) {
            return task.priority;
        }
    }
    return null;
}

或者使用 Stream-API:

public static Integer priority(String name) {
    return ALL_TASKS.stream()
            .filter(task -> task.name.equals(name))
            .map(task -> task.priority)
            .findFirst()
            .orElse(null);
}