知乎专栏 |
最常用的初始化方式,先创建一个list1,再给list1赋值。
List<String> list1 = new ArrayList<String>(); list1.add("apple"); list1.add("banana"); list1.add("orange");
使用一个List来初始化
List<String> list2 = new ArrayList<String>(Arrays.asList("apple", "banana", "orange"));
List<String> list3 = new ArrayList<String>(Collections.nCopies(2, "orange"));
使用匿名内部类来初始化
List<String> list4 = new ArrayList<String>() { { add("apple"); add("banana"); add("orange"); } };
初始化容量 initialCapacity
List<String> test = new ArrayList<>(5); IntStream.range(1, 10).forEach(value -> { test.add(String.valueOf(value)); }); System.out.println(test);
判断元素是否存在
import java.util.ArrayList; public class arraylist { public static void main(String[] args) { // TODO Auto-generated method stub ArrayList<String> whitelist = new ArrayList<String>(); whitelist.add("Neo"); whitelist.add("Jam"); whitelist.add("Sam"); if (whitelist.contains("Neo")) { System.out.println("Found!"); }else{ System.out.println("Not Found!"); } } }
package cn.netkiller.type; import java.util.ArrayList; import java.util.Iterator; import java.util.List; public class ArrayListExample { public static void main(String[] args) { // TODO Auto-generated method stub List<String> list = new ArrayList<String>(); list.add("Jack"); list.add("Jet"); list.add("Jack"); list.add("Mike"); list.add("Kitty"); list.add("Tom"); //while 循环 Iterator<String> it = list.iterator(); while (it.hasNext()) { System.out.println(it.next()); } for (Iterator<String> it1 = list.iterator(); it1.hasNext();) { System.out.println(it1.next()); } // for 循环 for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } // for 循环加强版 for (String i : list) { System.out.println(i); } } }
ArrayList 转为 Array
String[] array = {"/bin/sh","-c"}; List<String> list = new ArrayList<String>(Arrays.asList(array)); list.add("command"); list.add("param"); String[] command = (String[]) list.toArray(new String[0]); System.out.println(Arrays.toString(command));
List<String> list = new ArrayList<String>(); list.add("command"); list.add("param"); String listString = String.join(", ", list); System.out.println(listString);
List<String> list = new ArrayList<String>(); list.add("str1"); list.add("str2"); String[] array = (String[]) list.toArray(); System.out.println(array);
// create an ArrayList which going to // contains a list of Numbers ArrayList<Integer> Numbers = new ArrayList<Integer>(); // Add Number to list Numbers.add(23); Numbers.add(32); Numbers.add(45); Numbers.add(63); // forEach method of ArrayList and // print numbers Numbers.forEach((n) -> System.out.println(n));
import java.util.*; public class ArrayListTest { public static void main(String[] args) { // create an ArrayList which going to // contains a list of Student names which is actually // string values ArrayList<String> students = new ArrayList<String>(); // Add Strings to list // each string represents student name students.add("Ram"); students.add("Mohan"); students.add("Sohan"); students.add("Rabi"); // print result System.out.println("list of Students:"); // forEach method of ArrayList and // print student names students.forEach((n) -> print(n)); } // printing student name public static void print(String n) { System.out.println("Student Name is " + n); } }
List<String> arrayList = new ArrayList<>(); arrayList.add("A"); arrayList.add("B"); arrayList.add("C"); arrayList.add("D"); arrayList.add("E"); for (String item:arrayList){ System.out.println(item); } arrayList.forEach(item->System.out.println(item)); arrayList.forEach(System.out::println); arrayList.forEach(item->{ if("C".equals(item)){ System.out.println(item); } });
package cn.netkiller; import java.util.ArrayList; import java.util.List; public class Test { public Test(int id) { this.id = id; } public int id; public String name; public void setId(int id) { this.id = id; } public int getId() { return this.id; } public static void main(String[] args) throws InterruptedException { List<Test> arrayList = new ArrayList<Test>(); arrayList.add(new Test(1)); arrayList.add(new Test(2)); arrayList.add(new Test(3)); arrayList.add(new Test(4)); arrayList.add(new Test(5)); arrayList.forEach(item -> { System.out.println(item.getId()); item.setId(item.getId() + 1); }); arrayList.forEach(item -> { System.out.println(item.getId()); }); } }
arrayList.stream() .filter(s-> s.contains("B")||s.contains("C")) .forEach(System.out::println); arrayList.stream() .filter(s->s.contains("E")) .findFirst().ifPresent(s -> System.out.println(s));
ArrayList list = new ArrayList(); list.Add("aaa"); list.Add("bbb"); string[] arrString = (string[])list.ToArray(typeof( string)) ;
String str="1,2,3,4,5"; ArrayList b = new ArrayList( str.split(',') ) ;
ArrayList list = new ArrayList(); list.Add("aaa"); list.Add("bbb"); string str= string.Join(",", (string[])list.ToArray(typeof( string)));
List<byte[]> audios = new ArrayList<byte[]>(); public static byte[] concatenateByteArrays(List<byte[]> byteArrays) { ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); for (byte[] byteArray : byteArrays) { try { outputStream.write(byteArray); } catch (Exception e) { e.printStackTrace(); } } return outputStream.toByteArray(); }