前言:
最近的课程上学习了ArrayList,Arrays,HashMap和HashSet的使用方法,老师讲的特别清晰,受益颇多。整理下来,记录美好的岁月。注:方法在代码都有注释,清楚明白。
集合框架图:
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("张三");
list.add("李四");
list.add("wangwu");
//删除
list.remove(1);//根据索引删除
list.remove("wangwu");//根据内容删除
//更新
list.set(0, "zhangsan");//将索引为0的内容设置为'zhangsan'
//查询
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
//将数组转换为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);
//复制
int [] newarray = Arrays.copyOf(array, 4);//复制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");
//构造
//1
HashMap map1 = new HashMap();//默认大小为16
//2
HashMap map2 = new HashMap(18);//指定大小为18
//3
HashMap map3 = new HashMap(18,1);//指定大小为18和加载因子
//4
HashMap map4 = new HashMap(m);//将其他map传入
//大小
System.out.println(m.size());
//通过key取一个
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"));
//删除
m.remove("weight");
//修改
m.put("name","hly");
//查询
//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[]数组中的内容,将size设为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");
//删除
set.remove("wangwu");
//查询
//将内容给迭代器
Iterator it = set.iterator();
while(it.hasNext()) {//询问是否有下一个
String name = (String)it.next();
System.out.println(name);
}
}
}