Home > Java > javaTutorial > body text

Detailed explanation of conversion between java list, set, map and arrays

高洛峰
Release: 2017-01-22 15:31:38
Original
1504 people have browsed it

java list, set, map, detailed explanation of mutual conversion between arrays

1.list to set

Set set = new HashSet( new ArrayList());
Copy after login

2.set to list

List list = new ArrayList( new HashSet());
Copy after login

3. Convert the array to a list

List stooges = Arrays.asList( "Larry" , "Moe" , "Curly" );
Copy after login

At this time, there are three elements in stooges. Note: The add operation cannot be performed on the list at this time, otherwise "java.lang.UnsupportedOperationException" will be reported. Arrays.asList() returns a List, and it is a fixed-length List, so it cannot be converted to an ArrayList and can only be converted to AbstractList

The reason is that the asList() method returns the list form of an array. The returned list is just another view of the array, and the array itself does not disappear. Any operation on the list will eventually Reflected on the array. Therefore, the remove and add methods are not supported

String[] arr = { "1" , "2" };
List list = Arrays.asList(arr);
Copy after login

4. The array is converted to set

int [] a = { 1 , 2 , 3 };
Set set = new HashSet(Arrays.asList(a));
Copy after login

5.map related operate.

Map map = new HashMap();
map.put("1" , "a" );
map.put('2' , 'b' );
map.put('3' , 'c' );
System.out.println(map);
// 输出所有的值 
System.out.println(map.keySet());
// 输出所有的键 
System.out.println(map.values());
// 将map的值转化为List 
List list = new ArrayList(map.values());
System.out.println(list);
// 将map的值转化为Set 
Set set = new HashSet(map.values());
System.out.println(set);
Copy after login

6. List to array

List list = Arrays.asList( "a" , "b" );
System.out.println(list);
      
String[] arr = (String[])list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(arr));
Copy after login

Thank you for reading, I hope it can help everyone, thank you for your review of this article Site support!

For more detailed explanations of conversions between java list, set, map, and arrays, please pay attention to the PHP Chinese website!

Related labels:
source:php.cn
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Popular Tutorials
More>
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template
About us Disclaimer Sitemap
php.cn:Public welfare online PHP training,Help PHP learners grow quickly!