Java中常用的集合类、ArrayList 、HashMap及其遍历方法

淩亂°似流年 2024-02-17 19:52 15阅读 0赞

### 1 Java中常用的集合类 ###

### ![这里写图片描述][SouthEast] ###

![这里写图片描述][SouthEast 1]

### 2 ArrayList （类似：动态数组） ###

ArrayList al = new ArrayList();
    Clerk clerk1 = new Clerk("宋江", 23, 2000);
    Clerk clerk2 = new Clerk("吴用", 21, 1000);
    al.add(clerk1);
    al.add(clerk2);
    al.remove(1);
    
    System.out.println(al.size());
    
    for (int i = 0; i < al.size(); i++) {
        
        Clerk cl = (Clerk) al.get(i);
        System.out.println(cl.getName());
    }

### 3 HashMap ###

Clerk cl1 = new Clerk("name", 12, 1200);
    
    HashMap hm = new HashMap();
    
    hm.put("s001", cl1);
    
    if(hm.containsKey("s001")) {
    
        hm.get("s001");
    }
    
    Iterator it = hm.keySet().iterator(); // 使用迭代器遍历
    
    while (it.hasNext()) {
    
        String key = it.next().toString();
    
        Clerk cl = (Clerk) hm.get(key);
    
        System.out.println(cl.getName());
    }
    
    System.out.println(hm.size());

### 4 各种集合遍历方法 ###

// List
    for(Employee emp: department.getEmpList()) {
        System.out.println(department.getName() + " " + emp.getName());
    }
    // Set
    for(Employee emp: department.getEmpSet()) {
        System.out.println(department.getName() + " " + emp.getName());
    }
    // Map
    for(Entry<String, Employee> entry: department.getEmpMap().entrySet()) {
        System.out.println(entry.getKey() + " " + entry.getValue().getName());
    }

[SouthEast]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/7d668442024f4f7bb348411b01775bad.png
[SouthEast 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/6bc0160c39ee463e845553deb30e2bdb.png