容器深入研究--List的功能方法

Leefs 2020-01-14 AM 1800℃ 0条

# 容器深入研究--List的功能方法

### 前言

本篇讲述《Java编程思想》第17.5小节，List的功能方法

### 概述

正如你所看到的，基本的List很容易使用：大多数时候只是调用add()添加对象，使用get()一次取出一个元素，以及调用iterator()获取用于该序列的Iterator。

下面例子中每个方法都涵盖了一组不同的动作：basicTest()中包含每个List都可以执行的操作；iterMotion()使用Iterator遍历元素；对应的iterManipulation()使用Iterator修改元素；testVisual()用以查看List的操作效果；还有一些LinkedList专用的操作。

**代码示例**

```java
public class Lists {
    private static boolean b;
    private static String s;
    private static int i;
    private static Iterator<String> it;
    private static ListIterator<String> lit;
    public static void basicTest(List<String> a) {
        a.add(1, "x"); // 在位置1添加
        a.add("x"); // 在结尾添加
        // 添加一个集合
        a.addAll(Countries.names(25));
        // 从3开始添加一个集合
        a.addAll(3, Countries.names(25));
        b = a.contains("1"); // 是否存在
        // 整个集合都在里面吗
        b = a.containsAll(Countries.names(25));
        // 随机访问列表, ArrayList简单, LinkedList昂贵
        s = a.get(1); // Get (typed) object at location 1
        i = a.indexOf("1"); // Tell index of object
        b = a.isEmpty(); // Any elements inside?
        it = a.iterator(); // Ordinary Iterator
        lit = a.listIterator(); // ListIterator
        lit = a.listIterator(3); // Start at loc 3
        i = a.lastIndexOf("1"); // Last match
        a.remove(1); // Remove location 1
        a.remove("3"); // Remove this object
        a.set(1, "y"); // Set location 1 to "y"
        a.retainAll(Countries.names(25));
        a.removeAll(Countries.names(25));
        i = a.size();
        a.clear();
    }
    public static void iterMotion(List<String> a) {
        ListIterator<String> it = a.listIterator();
        b = it.hasNext();
        b = it.hasPrevious();
        s = it.next();
        i = it.nextIndex();
        s = it.previous();
        i = it.previousIndex();
    }
    public static void iterManipulation(List<String> a) {
        ListIterator<String> it = a.listIterator();
        it.add("47");
        // Must move to an element after add():
        it.next();
        // Remove the element after the newly produced one:
        it.remove();
        // Must move to an element after remove():
        it.next();
        // Change the element after the deleted one:
        it.set("47");
    }
    public static void testVisual(List<String> a) {
        System.out.println(a);
        List<String> b = Countries.names(25);
        System.out.println("b = " + b);
        a.addAll(b);
        a.addAll(b);
        System.out.println(a);
        // Insert, remove, and replace elements
        // using a ListIterator:
        ListIterator<String> x = a.listIterator(a.size()/2);
        x.add("one");
        System.out.println(a);
        System.out.println(x.next());
        x.remove();
        System.out.println(x.next());
        x.set("47");
        System.out.println(a);
        // Traverse the list backwards:
        x = a.listIterator(a.size());
        while(x.hasPrevious()) {
            System.out.println(x.previous() + " ");
        }
        System.out.println();
        System.out.println("testVisual finished");
    }
    // There are some things that only LinkedLists can do:
    public static void testLinkedList() {
        LinkedList<String> ll = new LinkedList<String>();
        ll.addAll(Countries.names(25));
        System.out.println(ll);
        // Treat it like a stack, pushing:
        ll.addFirst("one");
        ll.addFirst("two");
        System.out.println(ll);
        // Like "peeking" at the top of a stack:
        System.out.println(ll.getFirst());
        // Like popping a stack:
        System.out.println(ll.removeFirst());
        System.out.println(ll.removeFirst());
        // Treat it like a queue, pulling elements
        // off the tail end:
        System.out.println(ll.removeLast());
        System.out.println(ll);
    }
    public static void main(String[] args) {
        // Make and fill a new list each time:
        basicTest(
                new LinkedList<String>(Countries.names(25)));
        basicTest(
                new ArrayList<String>(Countries.names(25)));
        iterMotion(
                new LinkedList<String>(Countries.names(25)));
        iterMotion(
                new ArrayList<String>(Countries.names(25)));
        iterManipulation(
                new LinkedList<String>(Countries.names(25)));
        iterManipulation(
                new ArrayList<String>(Countries.names(25)));
        testVisual(
                new LinkedList<String>(Countries.names(25)));
        testLinkedList();
    }
}
```

> 运行结果

```
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
b = [ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, one, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
DJIBOUTI
EGYPT
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, one, 47, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
LESOTHO 
KENYA 
COTE D’IVOIR (IVORY COAST) 
BISSAU 
GUINEA 
GHANA 
THE GAMBIA 
GABON 
ETHIOPIA 
ERITREA 
EQUATORIAL GUINEA 
EGYPT 
DJIBOUTI 
CONGO 
COMOROS 
CHAD 
CENTRAL AFRICAN REPUBLIC 
CAPE VERDE 
CAMEROON 
BURUNDI 
BURKINA FASO 
BOTSWANA 
BENIN 
ANGOLA 
ALGERIA 
LESOTHO 
KENYA 
COTE D’IVOIR (IVORY COAST) 
BISSAU 
GUINEA 
GHANA 
THE GAMBIA 
GABON 
ETHIOPIA 
ERITREA 
EQUATORIAL GUINEA 
47 
one 
CONGO 
COMOROS 
CHAD 
CENTRAL AFRICAN REPUBLIC 
CAPE VERDE 
CAMEROON 
BURUNDI 
BURKINA FASO 
BOTSWANA 
BENIN 
ANGOLA 
ALGERIA 
LESOTHO 
KENYA 
COTE D’IVOIR (IVORY COAST) 
BISSAU 
GUINEA 
GHANA 
THE GAMBIA 
GABON 
ETHIOPIA 
ERITREA 
EQUATORIAL GUINEA 
EGYPT 
DJIBOUTI 
CONGO 
COMOROS 
CHAD 
CENTRAL AFRICAN REPUBLIC 
CAPE VERDE 
CAMEROON 
BURUNDI 
BURKINA FASO 
BOTSWANA 
BENIN 
ANGOLA 
ALGERIA

testVisual finished
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
[two, one, ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA, LESOTHO]
two
two
one
LESOTHO
[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI, CAMEROON, CAPE VERDE, CENTRAL AFRICAN REPUBLIC, CHAD, COMOROS, CONGO, DJIBOUTI, EGYPT, EQUATORIAL GUINEA, ERITREA, ETHIOPIA, GABON, THE GAMBIA, GHANA, GUINEA, BISSAU, COTE D’IVOIR (IVORY COAST), KENYA]
```

在basicTest()和iterMotion()方法中，调用只是为了演示正确的语法，虽然取得了返回值，却没有使用。某些情况则根本没有捕获返回值。

标签: Java, Java编程思想, 容器深入研究

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