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package cn.netkiller.example; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.LinkedList; import java.util.TreeSet; public class Test { public Test() { // TODO Auto-generated constructor stub } public static void main(String[] args) { // TODO Auto-generated method stub // A A B E F G C D String[] array = { "A", "A", "B", "E", "F", "G", "C", "D" }; Collection<String> list = new ArrayList<String>(Arrays.asList(array)); for (String str : list) { System.out.print(str + " "); } System.out.println(); // A A B E F G C D Collection<String> linkedList = new LinkedList<String>(Arrays.asList(array)); for (String str : linkedList) { System.out.print(str + " "); } System.out.println(); // 无重复,无序 D E F G A B C Collection<String> hashSet = new HashSet<String>(Arrays.asList(array)); for (String str : hashSet) { System.out.print(str + " "); } System.out.println(); // 无重复 A B C D E F G Collection<String> treeSet = new TreeSet<String>(Arrays.asList(array)); for (String str : treeSet) { System.out.print(str + " "); } System.out.println(); // 无重复 A B E F G C D Collection<String> linkedHashSet = new LinkedHashSet<String>(Arrays.asList(array)); for (String str : linkedHashSet) { System.out.print(str + " "); } } }
输出结果
A A B E F G C D A A B E F G C D A B C D E F G A B C D E F G A B E F G C D
public static List<String> list = new ArrayList<String>(); static { list.add("录入"); list.add("变更"); list.add("收藏"); list.add("在售"); list.add("展出"); }
var list = List.of("Java", "Python", "C"); var copy = List.copyOf(list); System.out.println(list == copy); // true
var list = new ArrayList<String>(); var copy = List.copyOf(list); System.out.println(list == copy); // false
数组转List
String[] arrays = {"tom", "jack", "kate"}; List<String> stringList= Stream.of(arrays).collect(Collectors.toList());
package cn.netkiller.demo; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class TestList { public TestList() { // TODO Auto-generated constructor stub } public static void main(String[] args) { List<String> list = Arrays.asList("1", "2", "3"); // jdk11 之前这样写 List<Integer> list1 = list.stream().map(Integer::parseInt).collect(Collectors.toList()); System.out.println(list1); // jdk16 现在可以这样写 List<Integer> list2 = list.stream().map(Integer::parseInt).toList(); System.out.println(list2); } }
List<String> inputStringList = Arrays.asList("Neo|Netkiller|Tom|Jerry".split("|")); List<String> wordsList = Arrays.asList("Neo|Tom".split("|")); System.out.println(inputStringList.containsAll(wordsList));
List<String> inputStringList = Arrays.asList("Neo|Netkiller|Tom|Jerry".split("|")); List<String> wordsList = Arrays.asList("Neo","Tom"); System.out.println(wordsList.stream().allMatch(inputStringList::contains));
List<String> list = Arrays.asList("a","b","c"); int index = (int) (Math.random()* list.size()); System.out.println(list.get(index));
使用 idea 写代码,list 变量可以看到 getFirst() / getLast() 但实际上 list 并没有两个方法,这时 idea 模版造成的。
java: 找不到符号 符号: 方法 getFirst() 位置: 类型为java.util.ArrayList<java.lang.String>的变量 list
// 创建一个ArrayList对象 ArrayList<String> list = new ArrayList<>(); // 添加元素到列表中 list.add("apple"); list.add("banana"); list.add("orange"); // 获取最后一个元素 // String firstElement = list.getFirst(); // String lastElement = list.getLast(); String lastElement = list.get(list.size() - 1); System.out.println("最后一个元素是:" + lastElement);
List<CompletableFuture<String>> completableFutures = Stream.of(future1, future2, future3).toList(); CompletableFuture[] completableFutureArray = completableFutures.toArray(CompletableFuture[]::new); List<CompletableFuture<String>> completableFutures = Stream.of(future1, future2, future3).toList(); var completableFutureArray = completableFutures.toArray(CompletableFuture[]::new);