Java List常用方法

最新推荐文章于 2024-12-05 11:05:43 发布

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#java #list #开发语言

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本文通过创建实体类UserBean和DeptBean，演示了如何使用ArrayList进行增删改查操作，并展示了如何利用Java 8 Stream API实现数据分组和排序。

导言:
后台开发Map和List的使用是家常便饭了,不过今天只是做个笔记,说下ArrayList的日常使用方法

知识点:

1,实体类UserBean

  //用户
  public class UserBean {
    private int userId;
    private String userName;
    private String deptId;
    private String deptName;
    private int sort;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getDeptId() {
        return deptId;
    }

    public void setDeptId(String deptId) {
        this.deptId = deptId;
    }

    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    public int getSort() {
        return sort;
    }

    public void setSort(int sort) {
        this.sort = sort;
    }

    @Override
    public String toString() {
        return "UserBean{" +
                "userId=" + userId +
                ", userName='" + userName + '\'' +
                ", deptId='" + deptId + '\'' +
                ", deptName='" + deptName + '\'' +
                ", sort=" + sort +
                '}';
    }

    public UserBean() {
    }

    public UserBean(int userId, String userName, String deptId, String deptName, int sort) {
        this.userId = userId;
        this.userName = userName;
        this.deptId = deptId;
        this.deptName = deptName;
        this.sort = sort;
    }

2,实体类DeptBean

  //部门
  public class DeptBean {
    private String deptId;
    private String deptName;
    private int sort;
    private List<UserBean> children = new ArrayList<>();

    public String getDeptId() {
        return deptId;
    }

    public void setDeptId(String deptId) {
        this.deptId = deptId;
    }

    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    public int getSort() {
        return sort;
    }

    public void setSort(int sort) {
        this.sort = sort;
    }

    public List<UserBean> getChildren() {
        return children;
    }

    public void setChildren(List<UserBean> children) {
        this.children = children;
    }
}

3,集合List使用

        List<UserBean> users = new ArrayList<>();
        //增 add,一个,addAll集合
        users.add(new UserBean(101, "张三", "d1002", "部门二", 2));
        users.add(new UserBean(102, "李四", "d1002", "部门二", 2));
        users.add(new UserBean(103, "王五", "d1001", "部门一", 1));
        users.add(new UserBean(104, "徐六", "d1003", "部门三", 3));
        users.add(new UserBean(105, "周琦", "d1003", "部门三", 3));
        List<UserBean> tempList = new ArrayList<>();
        tempList.add(new UserBean(106, "刘八", "d1001", "部门一", 1));
        tempList.add(new UserBean(107, "黄九", "d1004", "部门四", 4));
        tempList.add(new UserBean(108, "赵十", "d1004", "部门四", 4));
        tempList.add(new UserBean(109, "孙候", "d1004", "部门四", 4));
        tempList.add(new UserBean(110, "吴恩", "d1004", "部门四", 4));
        users.addAll(tempList);
        Log.i("listTest1", "所有: " + new Gson().toJson(users));
        Log.i("listTest", "-------------------------------------------------------------------------");
        //删 remove 110
        users.remove(users.size() - 1);
        Log.i("listTest2", "删除最后一个: " + new Gson().toJson(users));
        Log.i("listTest", "-------------------------------------------------------------------------");
        //改 set 101
        users.set(0, new UserBean(101, "钱万", "d1002", "部门二", 2));
        Log.i("listTest3", "更改101 : " + new Gson().toJson(users));
        Log.i("listTest", "-------------------------------------------------------------------------");
        //查 get 101
        UserBean userBean = users.get(0);
        Log.i("listTest4", "查询101 : " + userBean.toString());
        Log.i("listTest", "-------------------------------------------------------------------------");
        //索引位置 indexOf lastIndexOf
        users.indexOf(new UserBean(102, "李四", "d1002", "部门二", 2));
        //截取 subList 101-108
        List<UserBean> subList = users.subList(0, 7);
        //list 遍历
        for (int i = 0; i < subList.size(); i++) {
            Log.i("listTest5", "截取 : " + subList.get(i).toString());
        }
        Log.i("listTest", "-------------------------------------------------------------------------");
        //List分组 deptId
        Map<String, List<UserBean>> mapUser = users.stream().collect(Collectors.groupingBy(UserBean::getDeptId));

        List<DeptBean> deptBeans = new ArrayList<>();
        //map 遍历
        for (String key : mapUser.keySet()) {
            List<UserBean> userList = mapUser.get(key);
            DeptBean deptBean = new DeptBean();
            deptBean.setDeptId(key);
            deptBean.setSort(userList.get(0).getSort());
            deptBean.setDeptName(userList.get(0).getDeptName());

            List<UserBean> children = new ArrayList<>();
            //list 遍历
            for (UserBean mUserBean : userList) {
                UserBean u = new UserBean();
                u.setUserId(mUserBean.getUserId());
                u.setUserName(mUserBean.getUserName());
                children.add(u);
            }
            deptBean.setChildren(children);
            deptBeans.add(deptBean);
        }
        //List排序 sort
        List<DeptBean> deptBeanList = deptBeans.stream()
                .sorted(Comparator.comparing(DeptBean::getSort))
                .collect(Collectors.toList());
        Log.i("listTest6", new Gson().toJson(deptBeanList));