ArrayList对象转HashMap，arraylisthashmap

ArrayList对象转HashMap，arraylisthashmap

public static void main(String[] args) {
    Map<String, Map<String, String>> map = new HashMap<>();

    List<Dep> deps = new ArrayList<>();
    deps.add(new Dep("张三","2018-07","10"));
    deps.add(new Dep("张三","2018-06","43"));
    deps.add(new Dep("李四","2018-06","53"));
    deps.add(new Dep("王五","2018-07","37"));

    String[] dates = new String[deps.size()];
    int count = 0;
    for(Dep d : deps) {
        Map<String, String> temps = map.get(d.name);
        if(temps == null) {
            temps = new HashMap<>();
            map.put(d.name, temps);
        }
        temps.put(d.date, d.count);
        String date = d.date;
        dates[count ++] = d.date;
    }
    System.out.println("map--->>"+map);

    Set<String> set = new HashSet<>();
    for (int i = 0; i < dates.length; i ++) {
        set.add(dates[i]);
    }
    dates = (String[]) set.toArray(new String[set.size()]);

    Map<String, List<String>> result = new HashMap<>();
    for(Map.Entry<String, Map<String, String>> entry : map.entrySet()) {
        List<String> tempList = result.get(entry.getKey());
        if(tempList == null) {
            tempList = new ArrayList<>();
            result.put(entry.getKey(), tempList);
        }
        Map<String, String> tempMap = entry.getValue();
        for(String s : dates) {
            tempList.add(tempMap.get(s));
        }
    }
    System.out.println("result--->>"+result);
}


static class Dep {
    private String name;
    private String date;
    private String count;

    Dep(){

    }
    Dep(String name, String date, String count){
        this.name = name;
        this.date = date;
        this.count = count;
    }
}

 

输出结果：

map--->>{李四={2018-06=53}, 张三={2018-06=43, 2018-07=10}, 王五={2018-07=37}}
result--->>{李四=[53, null], 张三=[43, 10], 王五=[null, 37]}