2.2.3.List接口和实现类

特点: 有序、有下标、元素可以重复
方法
- void add(int index, Object o) // 在index位置插入对象o
- boolean addAll(int index, Collection c) //将一个集合中的元素添加到此集合中的index位置
- Object get(int index) // 返回集合中指定位置的元素
- List subList(int fromIndex, int toIndex) // 返回fromIndex和toIndex之间的集合元素

public class demo {
    public static void main(String[] args) {
        // 先创建集合对象
        List list = new ArrayList();
        // 添加元素
        list.add("苹果");
        list.add("小米");
        list.add(0, "华为");
        System.out.println("元素个数:" + list.size());
        System.out.println(list.toString());
        // 删除元素
        list.remove("苹果");
        System.out.println("删除之后:" + list.size());
        System.out.println(list.toString());
        // 遍历
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
        for (Object object: list) {
            System.out.println(object);
        }
        // 迭代器
        Iterator it = list.iterator();
        while (it.hasNext()) {
            System.out.println(it.next());
        }
        // 列表迭代器
        ListIterator lit = list.listIterator();
        System.out.println("列表迭代器,从前往后");
        while (lit.hasNext()) {
            System.out.println(lit.next());
            System.out.println(lit.nextIndex());
        }
        System.out.println("列表迭代器,从后往前");
        while (lit.hasPrevious()) {
            System.out.println(lit.previousIndex());
            System.out.println(lit.previous());
        }
        // 判断
        System.out.println(list.contains("苹果"));
        System.out.println(list.isEmpty());
        // 获取位置
        System.out.println(list.indexOf("华为"));
    }
}

public class demo {
    public static void main(String[] args) {
        // 创建集合
        List list = new ArrayList();
        list.add(20);
        list.add(30);
        list.add(40);
        list.add(50);
        list.add(60);
        System.out.println("元素个数:" + list.size());
        System.out.println(list.toString());
        // 删除操作
        list.remove(0);
        list.remove(new Integer(20));
        System.out.println("删除元素:" + list.size());
        System.out.println(list.toString());
        // 补充方法 subList, 含头不含尾
        List sublist = list.subList(1, 3);
        System.out.println(sublist);
    }
}

List实现类

ArrayList

数组结构实现,查询快,增删慢

运行效率快, 线程不安全

    package com.test.demo;
        
    import java.util.ArrayList;
    import java.util.Iterator;
    import java.util.ListIterator;
        
    public class demo4 {
        public static void main(String[] args) {
            // 创建结合
            ArrayList arrayList = new ArrayList();
            // 添加元素
            Student s1 = new Student("刘德华", 20);
            Student s2 = new Student("郭富城", 30);
            Student s3 = new Student("梁朝伟", 40);
            arrayList.add(s1);
            arrayList.add(s2);
            arrayList.add(s3);
            System.out.println("元素个数:" + arrayList.size());
            System.out.println(arrayList.toString());
            // 删除元素
            // arrayList.remove(s1);
            // 正常new的是删不掉的，需要重写equals
            arrayList.remove(new Student("刘德华", 20));
            System.out.println("元素个数:" + arrayList.size());
            System.out.println(arrayList.toString());
            // 遍历
            Iterator it = arrayList.iterator();
            while (it.hasNext()) {
                Student s = (Student)it.next();
                System.out.println(s.toString());
            }
            ListIterator lit = arrayList.listIterator();
            while (lit.hasNext()) {
                Student s = (Student)lit.next();
                System.out.println(s.toString());
            }
            while (lit.hasPrevious()) {
                Student s = (Student)lit.previous();
                System.out.println(s.toString());
            }
            // 判断
            System.out.println(arrayList.contains(new Student("梁朝伟", 40)));
            System.out.println(arrayList.isEmpty());
            // 查询
            System.out.println(arrayList.indexOf(s1));
        }
        
        static class Student {
            private String name;
            private int age;
            public Student(String name, int age) {
                this.name = name;
                this.age = age;
            }
        
            public String getName() {
                return name;
            }
        
            public void setName(String name) {
                this.name = name;
            }
        
            public int getAge() {
                return age;
            }
        
            public void setAge(int age) {
                this.age = age;
            }
        
            @Override
            public String toString() {
                return "Student{" +
                        "name='" + name + '\'' +
                        ", age=" + age +
                        '}';
            }
        
            @Override
            public boolean equals(Object obj) {
                // 1.判断是不是同一个对象
                if (this == obj) {
                    return true;
                }
                // 2.判断是否为空
                if (obj == null) {
                    return false;
                }
                // 3.判断是否是Student类型
                if (obj instanceof Student) {
                    Student s = (Student)obj;
                    // 4.比较属性
                    if (this.name.equals(s.getName()) && this.age == s.getAge()) {
                        return true;
                    }
                }
                return false;
            }
        }
    }

源码

DEFAULT_CAPACITY = 10; 默认容量 
    注意:如果没有向集合中添加任何元素时,size为0，容量为0
elementData 存放元素的数组 
size 实际元素个数
add() 添加元素
   //todo::待补充

Vector

数组结构实现,查询快,增删慢
效率快, 线程安全

public class demo {
    public static void main(String[] args) {
        // 创建集合
        Vector vector = new Vector();
        vector.add("草莓");
        vector.add("芒果");
        vector.add("西瓜");
        System.out.println("元素个数:" + vector.size());
        // 删除
        vector.remove(0);
        vector.remove("西瓜");
        vector.clear();
        // 使用枚举器
        Enumeration en = vector.elements();
        while (en.hasMoreElements()) {
            String o = (String)en.nextElement();
            System.out.println(o);
        }
        // 判断
        vector.contains("西瓜");
        vector.isEmpty();
        // vector其它方法
        vector.lastElement();
    }
}

LinkedList

链表结构实现,增删快,查询慢

  public class demo {
      public static void main(String[] args) {
          // 创建结合
          LinkedList linkedList = new LinkedList();
          // 添加
          Student s1 = new Student("刘德华", 20);
          Student s2 = new Student("郭富城", 20);
          Student s3 = new Student("梁朝伟", 20);
          linkedList.add(s1);
          linkedList.add(s2);
          linkedList.add(s3);
          System.out.println("元素个数" + linkedList.size());
          System.out.println(linkedList);
          // 删除
          linkedList.remove(s1);
          linkedList.remove(new Student("郭富城", 20));
          System.out.println(linkedList.size());
         // linkedList.clear();
          // 遍历
          for (int i = 0; i < linkedList.size(); i++) {
              System.out.println(linkedList.get(i));
          }
          for (Object object: linkedList) {
              Student s = (Student)object;
              System.out.println(s.toString());
          }
          Iterator it = linkedList.iterator();
          while (it.hasNext()) {
              Student s = (Student) it.next();
              System.out.println(s.toString());
          }
          ListIterator lit = linkedList.listIterator();
          while (lit.hasNext()) {
              Student s = (Student) lit.next();
              System.out.println(s.toString());
          }
          // 判断
          System.out.println(linkedList.contains(s1));
          System.out.println(linkedList.isEmpty());
          // 获取
          System.out.println(linkedList.indexOf(s2));
          System.out.println(linkedList.indexOf(s3));
      }
  }