java集合之Map键值与Set、List、数组转换

看了别人写的文章后，自己总结了一下，然后写了一篇demo

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Demo_2 {
	public static void main(String[] args) {
		Demo_2 d=new Demo_2();
		d.mapToSet();
		d.mapToList();
		d.setToList();
		d.listToSet();
		d.listToArr();
		d.arrToList();
		d.setToArr();
		d.arrToSet();
	}
	public void mapToSet() {
		Map<String,String> map=new HashMap<String,String>();
		map.put("1", "one");
		map.put("2", "two");
		map.put("3", "tree");
		Set<String> set=map.keySet();
		System.out.println("map--set"+set);
		Set<String> set1=new HashSet<String>(map.values());
		System.out.println("map--set"+set1);
	}
	public void mapToList() {
		Map<String,String> map=new HashMap<String,String>();
		map.put("1", "one");
		map.put("2", "two");
		map.put("3", "tree");
		List<String> list = new ArrayList<String>(map.keySet());
		System.out.println("map--list"+list);
		List<String> list1= new ArrayList<String>(map.values());
		System.out.println("map--list"+list1);
	}
	public void setToList() {
		Set<String> set=new HashSet<String>();
		set.add("a");
		set.add("b");
		set.add("c");
		List<String> list = new ArrayList<String>(set);
		System.out.println("set--list"+list);
	}
	public void listToSet() {
		List<String> list = new ArrayList<String>();
		list.add("a");
		list.add("b");
		list.add("c");
		Set<String> set= new HashSet<String>(list);
		System.out.println("list--set"+set);
	}
	public void listToArr() {
		List<String> list = new ArrayList<String>();
		list.add("a");
		list.add("b");
		list.add("c");
		String[] arr=new String[list.size()];
		list.toArray(arr);
		System.out.println("list--arr"+Arrays.toString(arr));
	}
	public void arrToList() {
		String[] arr= {"ab","ac","bc"};
		List<String> list= new ArrayList<String>();
		list=Arrays.asList(arr);
		System.out.println("arr--list"+list);
	}
	public void setToArr() {
		Set<String> set=new HashSet<String>();
		set.add("a");
		set.add("b");
		set.add("c");
		String[] arr=new String[set.size()];
		set.toArray(arr);
		System.out.println("set--arr"+Arrays.toString(arr));
	}
	public void arrToSet() {
		String[] arr= {"ab","ac","bc"};
		Set<String> set= new HashSet<String>(Arrays.asList(arr));
		System.out.println("arr--set"+set);
	}
}

涉及的转换方法有利用构造器，aslist，toArray，keySet等方法