JDK-In-Action-ArrayList

ArrayList

List接口的具体实现,底层基于Object[]存储元素,可自动扩容,元素可为null,非线程安全.
优势:随机访问操作只需常量时间;
劣势:随机插入,随机删除,新增大量元素的操作需要线性时间;

API Example

元素替换和查找

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 2, 2, 5));

 data.set(1, 0);
 assertEquals(data, "[1, 0, 2, 2, 5]");

 int i = data.indexOf(2);
 assertEquals(i, 2);

 i = data.lastIndexOf(2);
 assertEquals(i, 3);

 boolean contains = data.contains(2);
 assertTrue(contains);

 contains = data.contains(3);
 assertTrue(!contains);

 contains = data.containsAll(Arrays.asList(2, 5));
 assertTrue(contains);

指定容量的构造函数

 List<String> initCapacityList = new ArrayList<>(2);
 assertEquals(initCapacityList, "[]");

静态构造不可变的 List

 //java.util.Arrays.ArrayList
 List<String> list = Arrays.asList("one", "two");
 try {
     list.add("three");
     assertFail();
 } catch (UnsupportedOperationException e) {
     e.printStackTrace(System.out);
 }

java.lang.UnsupportedOperationException
 at java.util.AbstractList.add(AbstractList.java:148)
 at java.util.AbstractList.add(AbstractList.java:108)
 at com.gitee.zhwcong.collections.ArrayListExample.静态构造不可变的List(ArrayListExample.java:44)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 at java.lang.reflect.Method.invoke(Method.java:498)
 at com.gitee.zhwcong.Utils.runExampleMethod(Utils.java:41)
 at com.gitee.zhwcong.collections.ArrayListExample.main(ArrayListExample.java:15)

新增和插入元素

 List<String> data = new ArrayList<>();
 //新增
 data.add("one");
 data.addAll(Arrays.asList("three", "four"));
 //插入
 data.add(0, "zero");
 data.add(1, "two");
 assertEquals(data, "[zero, two, one, three, four]");
 //批量插入
 data.addAll(4, Arrays.asList("five", "six"));
 assertEquals(data, "[zero, two, one, three, five, six, four]");

删除和清空列表

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));

 data.remove(0);
 assertEquals(data, "[2, 3, 4, 5]");

 data.remove(3);
 assertEquals(data, "[2, 3, 4]");

 data.clear();
 assertEquals(data, "[]");

指定初始集合的构造函数

 Collection<String> data = new ArrayList<>();
 data.add("one");
 List<String> initDataList = new ArrayList<>(data);
 assertEquals(initDataList, "[one]");

单线程中的并发修改异常

 List<Integer> list = new ArrayList<>();
 list.addAll(Arrays.asList(1, 2, 3, 4, 5));
 Iterator<Integer> iterator = list.iterator();
 while (iterator.hasNext()) {
     Integer next = iterator.next();
     iterator.remove();
     //这里任何对list的更新都会导致`ConcurrentModificationException`
// list.remove(next);
// list.add(1);
 }

复制所有元素到对象数组

 List<Integer> data = Arrays.asList(1, 2, 3, 4, 5);
 Object[] objects = data.toArray();
 assertEquals(objects, "[1, 2, 3, 4, 5]");

复制所有元素到整数类型数组

 List<Integer> data = Arrays.asList(1, 2, 3, 4, 5);
 Integer[] a = new Integer[0];
 Integer[] ints = data.toArray(a);
 assertEquals(ints, "[1, 2, 3, 4, 5]");
 assertTrue(a.length == 0);

 //仅当参数数组的空间足够拷贝所有元素时参数a才会被填充值
 a = new Integer[data.size()];
 ints = data.toArray(a);
 assertEquals(a, "[1, 2, 3, 4, 5]");
 assertEquals(ints, "[1, 2, 3, 4, 5]");

空构造函数

 List<String> emptyList = new ArrayList<>();
 assertEquals(emptyList, "[]");

列表排序

 List<Integer> data = new ArrayList<>(Arrays.asList(9, 2, 7, 3, 1));

 System.out.println("自然顺序");
 Collections.sort(data);
 assertEquals(data, "[1, 2, 3, 7, 9]");

 System.out.println("逆序");
 Collections.sort(data, (o1, o2) -> o2 - o1);
 assertEquals(data, "[9, 7, 3, 2, 1]");

自然顺序
逆序

For循环迭代元素

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
 for (int i = 0; i < data.size(); i++) {
     System.out.println(data.get(i));
 }

1
2
3
4
5

Foreach Stream迭代元素

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
 data.forEach(System.out::println);

1
2
3
4
5

List Iterator迭代元素

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3));
 ListIterator<Integer> listIterator = data.listIterator();
 System.out.println("next is 1:" + listIterator.next());
 listIterator.add(5);
 assertEquals(data, "[1, 5, 2, 3]");

 System.out.println("next is 2:" + listIterator.next());
 System.out.println("previous is 2:" + listIterator.previous());
 listIterator.remove();
 assertEquals(data, "[1, 5, 3]");

next is 1:1
next is 2:2
previous is 2:2

Foreach迭代元素

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
 for (Integer e : data) {
     System.out.println(e);
 }

1
2
3
4
5

Iterator迭代元素

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
 Iterator<Integer> iterator = data.iterator();
 while (iterator.hasNext()) {
     System.out.println(iterator.next());
 }

1
2
3
4
5

列表切片视图

 List<Integer> data = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
 System.out.println("生成一个共享底层数组的视图");
 List<Integer> subList = data.subList(1, 4);
 assertEquals(subList, "[2, 3, 4]");
 subList.add(6);
 assertEquals(subList, "[2, 3, 4, 6]");
 assertEquals(data, "[1, 2, 3, 4, 6, 5]");

生成一个共享底层数组的视图

引用

• 示例源码下载
• JDK8 java.util.ArrayList Source Code