Java进阶总结——Map和Collections
1.Map
1.1 HashMap
package day21.map;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Set;
public class HashMapDemo {
public static void main(String[] args) {
//1.初始化一个HashMap对象
HashMap<Integer, Integer>map=new HashMap<Integer, Integer>();
//2.添加数据
map.put(0, 151);
map.put(1, 152);
map.put(3, 153);
map.put(2, 154);
map.put(null, 111);
map.put(4, 0);
System.out.println(map.toString());
//3.修改
map.put(null, 154);
System.out.println(map.toString());
//4.删除元素，通过key删除value
map.remove(null);
System.out.println(map.toString());
//5.查看成员
//通过key获取value
System.out.println(map.get(3));
//判断是否包含指定的key值
System.out.println(map.containsKey(null));
//判断是否包含value值
System.out.println(map.containsValue(152));
//查看键值对的个数
System.out.println(map.size());
//获取所有的key值
System.out.println("key值");
Set<Integer>keys=map.keySet();
for (Integer integer : keys) {
System.out.print(integer+"\t");
}
System.out.println();
System.out.println("value值");
//获取到所有的value值
Collection<Integer>values=map.values();
for (Integer integer : values) {
System.out.print(integer+"\t");
}
System.out.println();
//获取所有的映射关系，进行遍历map
Set<Entry<Integer, Integer>>en=map.entrySet();
for (Entry<Integer, Integer> entry : en) {
System.out.print(entry.getKey()+"--"+entry.getValue());
System.out.println();
}
}
}
输出结果：
1.2TreeMap
package day21.map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;
public class TreeMapDemo {
public static void main(String[] args) {
//初始化一个TreeMap对象
TreeMap<Integer, String>map=new TreeMap<Integer, String>();
//添加
map.put(6, "浪子一秋");
map.put(2, "一叶知秋");
map.put(1, "葬剑山庄");
map.put(9, "武林至尊");
map.put(4, "葬剑灬尊");
System.out.println(map.toString());
//取值
System.out.println(map.firstEntry());
//获取所有元素
Set<Entry<Integer, String>>en=map.entrySet();
for (Entry<Integer, String> entry : en) {
System.out.print(entry.getKey()+"\t"+entry.getValue());
System.out.println();
}
System.out.println(map.floorEntry(3));
}
}
输出结果：
2.Collections
package day21.map;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class CollectionsDemo {
public static void main(String[] args) {
//向指定的列表中添加元素
ArrayList<String>list=new ArrayList<String>();
Collections.addAll(list,"id ","name","age","sex");
System.out.println(list.toString());
//使用二分查找法查找指定元素
System.out.println(Collections.binarySearch(list, "sex"));
//将列表中的元素复制到另一个列表中
ArrayList<String>dest=new ArrayList<String>();
Collections.addAll(dest,"id1 ","name","age","sex","nn");
Collections.copy(dest, list);
System.out.println(dest.toString());
//反转顺序
Collections.reverse(dest);
System.out.println(dest.toString());
//获取最值,assic码值
System.out.println(Collections.max(dest));
System.out.println(Collections.min(dest));
//比较器
Collections.reverseOrder();
System.out.println(dest.toString());
//Collections.reverseOrder(Comparator<String>cmp);
//填充元素
Collections.fill(dest,"score");
System.out.println(dest.toString());
}
}
输出结果：
3.知识框架