java基础对集合的理解

集合

Collection类：主要了解ArrayList，LinkedList；HashSet，TreeSet；

Map类：HashMap，TreeMap；

提供对集合的基本操作，如何遍历一个集合，定义一个集合的泛型。

①.

package com.itheima.study.collection;


import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;


public class ArrayListDemo
{
public static void main(String[] args)
{
//定义存放String类型的容器
List<String> list = new ArrayList<String>();

//添加元素
list.add("张三");
list.add("李四");
list.add("王五");
list.add("前六");
list.add("孙七");
list.add("王五");
//第一种遍历方式
for(int i = 0; i < list.size(); i++)
{
System.out.print(list.get(i) + "  ");
}

//移除集合中第一个元素
list.remove(0);
System.out.println();
System.out.println("---------------------------");

//迭代(第二种遍历方式)
for(Iterator<String> ite = list.listIterator(); ite.hasNext();)
{
System.out.print(ite.next() + "  ");
}

//移除内容为孙七的元素
list.remove("孙七");
System.out.println();
System.out.println("---------------------------");
//第三种遍历方式，增强的for循环
for (String string : list)
{
System.out.print(string + "  ");
}



}
}

②.

package com.itheima.study.collection;


import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;


public class LinkedListDemo
{
public static void main(String[] args)
{
List<String> list = new LinkedList<String>();
//想list中添加元素
list.add("张三");
list.add("前六");
list.add(1, "阿九");
list.add("李四");
list.add("王五");
System.out.println(list);
//使用LinkeList的扩展方法必须向下类型转换为LinkedList
LinkedList<String> linkedList = (LinkedList<String>)list;
//添加元素到首位
linkedList.addFirst("孙七");
//添加元素到最后
linkedList.addLast("人人影视");
linkedList.addLast("人人影视");
System.out.println(linkedList);
//移除元素
linkedList.remove(linkedList.size() - 1);
System.out.println(list);
//第一种遍历方式增强的for循环
for (String string : linkedList)
{
System.out.print(string + "   ");
}
System.out.println();
System.out.println("----------------------------");
//第二种遍历方式 for循环
for(int i = 0; i < linkedList.size(); i++)
{
System.out.print(linkedList.get(i) + "   ");
}
System.out.println();
System.out.println("----------------------------");

//第三种遍历方式迭代
for(Iterator<String> ite = linkedList.iterator(); ite.hasNext();)
{
System.out.print(ite.next() + "   ");
}
System.out.println();
System.out.println("----------------------------");
linkedList.clear();
System.out.println(linkedList);

}
}

③.

package com.itheima.study.collection;


import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;


public class HashSetDemo
{
public static void main(String[] args)
{
Set<String> set = new HashSet<String>();
//增加元素
set.add("张三");
set.add("李四");
set.add("王五");
set.add("前六");
System.out.println(set.add("人人影视"));
//结果为false表明重复元素不能加入set中
System.out.println(set.add("人人影视"));

//第一种遍历方式 迭代方式
for(Iterator<String> ite = set.iterator(); ite.hasNext();)
{
System.out.print(ite.next() + "   ");
}
System.out.println();
System.out.println("---------------------------------------");
set.remove("人人影视");
//第二中遍历方式 争强的for循环
for (String string : set)
{
System.out.print(string + "   ");
}
System.out.println();
System.out.println("---------------------------------------");

}
}

④.

package com.itheima.study.collection;


import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;


public class TreeSetDemo
{
public static void main(String[] args)
{
Set<Integer> set = new TreeSet<Integer>();
//添加元素
set.add(9);
set.add(11);
set.add(5);
set.add(4);
set.add(11);
System.out.println(set);
//第一种遍历方式
//结果为按顺序排列的默认是从小到大
for (Integer integer : set)
{
System.out.print(integer + "   ");
}
System.out.println();
System.out.println("-----------------------------");

//第二种遍历方式
for(Iterator<Integer> ite = set.iterator(); ite.hasNext();)
{
System.out.print(ite.next() + "   ");
}
}
}

⑤.

package com.itheima.study.collection;


import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;


public class HashMapDemo
{
public static void main(String[] args)
{
Map<Integer, String> map = new HashMap<Integer,String>();
//添加元素
map.put(1, "张三");
map.put(2, "李四");
map.put(6, "王五");
map.put(4, "前六");
System.out.println(map);

//得到Map.Entry集合
Set<Map.Entry<Integer, String>> set = map.entrySet();
//遍历set
for (Map.Entry<Integer, String> entry : set)
{
System.out.print(entry.getKey() + ":" + entry.getValue() + "     ");
}
System.out.println();
System.out.println("------------------------------");

//遍历set
for(Iterator<Map.Entry<Integer, String>> ite = set.iterator(); ite.hasNext();)
{
Map.Entry<Integer, String> entry = ite.next();
System.out.print(entry.getKey() + ":" + entry.getValue() + "     ");
}

System.out.println();
System.out.println("------------------------------");

//得到KeySet的集合
Set<Integer> keySet = map.keySet();
//遍历集合
for (Integer integer : keySet)
{
System.out.print(integer + ":" + map.get(integer) + "     ");
}
System.out.println();
System.out.println("-------------------------------");
//迭代keySet集合
for(Iterator<Integer> ite = keySet.iterator(); ite.hasNext();)
{
Integer key = ite.next();
System.out.print(key + ":" + map.get(key) + "     ");
}

}
}

⑥.

package com.itheima.study.collection;


import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;


public class TreeMapDemo
{
public static void main(String[] args)
{
Map<Integer, String> map = new TreeMap<Integer,String>();
//添加元素
map.put(1, "zhangsan");
map.put(2, "lisi");
map.put(6, "wangwu");
map.put(4, "qianliu");
System.out.println(map);

//得到Map.Entry集合
Set<Map.Entry<Integer, String>> set = map.entrySet();
//遍历set
for (Map.Entry<Integer, String> entry : set)
{
System.out.print(entry.getKey() + ":" + entry.getValue() + "     ");
}
System.out.println();
System.out.println("------------------------------");

//遍历set
for(Iterator<Map.Entry<Integer, String>> ite = set.iterator(); ite.hasNext();)
{
Map.Entry<Integer, String> entry = ite.next();
System.out.print(entry.getKey() + ":" + entry.getValue() + "     ");
}

System.out.println();
System.out.println("------------------------------");

//得到KeySet的集合
Set<Integer> keySet = map.keySet();
//遍历集合
for (Integer integer : keySet)
{
System.out.print(integer + ":" + map.get(integer) + "     ");
}
System.out.println();
System.out.println("-------------------------------");
//迭代keySet集合
for(Iterator<Integer> ite = keySet.iterator(); ite.hasNext();)
{
Integer key = ite.next();
System.out.print(key + ":" + map.get(key) + "     ");
}

}
}