常用集合类操作

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ArrayList

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ArrayList list=new ArrayList();	
User zhangsan=new User("张三",1);	
list.add(zhangsan);	
Dog dog=new Dog();	
dog.setName("哈哈");	
dog.setAge(1);	
list.add(dog);	
for (Object object : list) {	
	if(object instanceof User){	
		User user=(User)object;	
		System.out.println(user.getName());	
	}else{	
		Dog user=(Dog)object;	
		System.out.println(user.getName());		
	}	
}
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ArrayList list=new ArrayList();
list.add("a");
list.add("男");
list.add("a");
//add(index,object)方式插入时要注意插入的位置不能越界
list.add(3,"张三");
System.out.println(list);//[a, 男, a, 张三]
list.set(1,"女");
System.out.println(list);//[a, 女, a, 张三]
//根据位置来删除
list.remove("a");
System.out.println(list);//[女, a, 张三]
list.remove(1);
System.out.println(list);//[女, 张三]
System.out.println(list.get(1));//张三
//集合的大小
System.out.println(list.size());//2

LinkedList

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LinkedList list=new LinkedList();
for(int i=1;i<=200;i++){
    list.add(i);
}
list.addFirst(new User("张三",1));
int count=1;
while(list.size()!=1){
    if(count%3==0){
        list.removeFirst();
    }else{
        list.addLast(list.removeFirst());
    }
    count++;
}
System.out.println(list.getFirst());

HashMap

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HashMap<String, String> hm=new HashMap<String,String>();
hm.put("name", "张三");
hm.put("age", "18");
System.out.println(hm.get("name"));
hm.remove("name1");
System.out.println(hm.get("name"));
Set<String> keys=hm.keySet();
for (String string : keys) {
	System.out.println(string+"--"+hm.get(string));
}
for(String value:hm.values()){
	System.out.println(value);
}
Set<Entry<String, String>> entries=hm.entrySet();
for (Entry<String, String> entry : entries) {
	System.out.println(entry.getValue());
	System.out.println(entry.getKey());
}

HashSet

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HashSet hs=new HashSet();
hs.add("a");
hs.add("b");
hs.add("c");
HashSet hs1=new HashSet();
hs1.add("e");
hs1.add("d");
hs1.add("c");
hs.addAll(hs1);
//去重的方法
System.out.println(hs.size());
Iterator it=hs.iterator();
while(it.hasNext()){
	System.out.println(it.next());
}
System.out.println("*************");
//for(集合中每个元素的类型 对应元素的形参 : 集合)
for (Object object : hs) {
	System.out.println(object);
}

其他

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List list=Arrays.asList(3,4,2,5,1,6,8);
Collections.sort(list);
System.out.println(list);

System.arraycopy(integers,0,newIntegersArray,0,integers.length);

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