java集合：簡單使用ArrayList，Arrays，HashMap，HashSet

前言：

最近的課程上學習了ArrayList，Arrays，HashMap和HashSet的使用方法，老師講的特別清晰，受益頗多。整理下來，記錄美好的歲月。注：方法在代碼都有註釋，清楚明白。

集合框架圖：

1.ArrayList：

package JCF;

import java.util.ArrayList;

public class arraylist {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ArrayList<String> list = new ArrayList<String>();
		//添加
		list.add("張三");
		list.add("李四");
		list.add("wangwu");
		
		//刪除
		list.remove(1);//根據索引刪除
		list.remove("wangwu");//根據內容刪除
		
		//更新
		list.set(0, "zhangsan");//將索引爲0的內容設置爲'zhangsan'
		
		//查詢
		for(int i=0;i<list.size();i++) {
			System.out.println(list.get(i));
		}
	}
}

2.Arrays：

package JCF;

import java.util.Arrays;
import java.util.List;

public class arrays {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		//將數組轉換爲list
		List<String> list = Arrays.asList("a","b","c","d");
		
		int [] array = {4,8,1,3,7,6,5};
		//排序
		Arrays.sort(array);
		for(int i=0;i<array.length;i++){
			System.out.print(array[i]+" ");
		}
		System.out.println();
		
		//二分查找
		int index = Arrays.binarySearch(array, 7);//二分查找7的索引
		System.out.println(index);
		
		//複製
		int [] newarray = Arrays.copyOf(array, 4);//複製array的前四位
		for(int i=0;i<newarray.length;i++) {
			System.out.print(newarray[i]+" ");
		}
	}
}

3.HashMap：

package JCF;

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

public class hashmap {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		HashMap m = new HashMap();
		m.put("age","19");
		m.put("name", "wwx");
		m.put("phone", "63456565465");
		m.put("weight", "130");
		
		//構造
		//1
		HashMap map1 = new HashMap();//默認大小爲16
		//2
		HashMap map2 = new HashMap(18);//指定大小爲18
		//3
		HashMap map3 = new HashMap(18,1);//指定大小爲18和加載因子
		//4
		HashMap map4 = new HashMap(m);//將其他map傳入

		//大小
		System.out.println(m.size());
		
		//通過key取一個
		String name = (String)m.get("name");
		System.out.println(name);
		
		//是否包含
		System.out.println("containsKey:"+m.containsKey("age"));
		System.out.println("containsValue:"+m.containsValue("hly"));
		
		//刪除
		m.remove("weight");
		
		//修改
		m.put("name","hly");
		
		//查詢
		//1
		Set set = m.keySet();
		Iterator it = set.iterator();
		
		while(it.hasNext()) {
			
			String key = (String)it.next();
			String value = (String)m.get(key);
			System.out.println(key+"======="+value);
		}
		//2
		set = m.entrySet();
		it = set.iterator();
		
		while(it.hasNext()) {
			Entry entry = (Entry)it.next();
			System.out.println(entry.getKey()+"=="+entry.getValue());;
		}
		//3
		Collection coll = m.values();
		for(Object object:coll) {
			System.out.println(object);
		}
		
		//清空
		m.clear();//清空m中entry[]數組中的內容，將size設爲0
		
		//判空
		System.out.println(m.isEmpty());
	}
}

4.HashSet：

package JCF;

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

public class hashset {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		HashSet set = new HashSet();
		
		//添加
		set.add("lisi");
		set.add("wangwu");
		set.add("maliu");
		
		//修改
		set.remove("lisi");
		set.add("lisi2");
		
		//刪除
		set.remove("wangwu");
		
		//查詢
		//將內容給迭代器
		Iterator it = set.iterator();
		while(it.hasNext()) {//詢問是否有下一個
			String name = (String)it.next();
			System.out.println(name);
		}
	}
}