黑马程序员 Java集合（1）Collection集合

集合和数组的区别：

数组可以存储基本数据类型和对象，但是数组的长度是不变的。集合只能存储对象，长度是可变的。

Java集合主要由两个接口派生而来的：Collection和Map。

Collection接口

boolean add(E e)
boolean addAll(Collection c)
void clear() 清除集合里的所有元素，将集合长度变为0
boolean contains(E e)
boolean containsAll(Collection c)
boolean isEmpty()
Iterator iterator() 返回一个Iterator对象用于遍历集合
boolean remove(E e)
boolean removeAll(Collection)
boolean retainAll(Collection c) 从集合中删除集合c里不包含的元素。
int size()
Object toArray() 将集合转换为数组

 1 import java.util.*;
 2 class  CollectionDemo
 3 {
 4     public static void main(String[] args) 
 5     {
 6         ArrayList tree= new ArrayList();
 7         tree.add("杨树");
 8         tree.add("桃树");
 9         tree.add("柳树");
10         tree.add("梨树");
11         ArrayList fruiter =new ArrayList();
12         fruiter.add("桃树");
13         fruiter.add("葡萄树");
14         fruiter.add("梨树");
15         fruiter.add("杏树");
16         tree.retainAll(fruiter);
17         System.out.println(tree);
18     }
19 }
20 //运行结果 [桃树, 梨树]

Iterator接口

boolean hasNext()
Object next() 返回集合里的下一个元素
void remove()返回集合里next()上一次返回的元素

 1 import java.util.*;
 2 class  CollectionDemo
 3 {
 4     public static void main(String[] args) 
 5     {
 6         ArrayList tree= new ArrayList();
 7         tree.add("杨树");
 8         tree.add("桃树");
 9         tree.add("柳树");
10         tree.add("梨树");
11         Iterator it=tree.iterator();
12         while (it.hasNext())
13         {
14             System.out.println(it.next());
15         }
16     }
17 }
18 /*
19 杨树
20 桃树
21 柳树
22 梨树
23 */

List接口方法摘要

void add(int index,E element)
boolean addAll(int index,Collection c)
E get(int index) 返回index索引的元素
int indexOf(Object o)返回元素o第一次出现的索引
int lastIndexOf(Object o)
Object remove(int index)删除并返回index索引处的元素
E set(int index,E element)将索引index的元素替换为element并返回新元素。
List subList(int fromIndex,int toIndex)包含头不包含尾

 1 import java.util.*;
 2 class  CollectionDemo
 3 {
 4     public static void main(String[] args) 
 5     {
 6         ArrayList tree= new ArrayList();
 7         tree.add("杨树");
 8         tree.add("桃树");
 9         tree.add("柳树");
10         tree.add("梨树");
11         System.out.println(tree.subList(0,2));//[杨树, 桃树]
12 
13     }
14 }

ListIterator接口

ListIterator是接口Iterator子接口

方法摘要

boolean hasPrevious() 返回该迭代器关联的集合是否还有上一个元素
E previous返回列表的前一个元素
void add(E e)将指定元素插入列表
void remove()

import java.util.*;
class  CollectionDemo
{
    public static void main(String[] args) 
    {
        ArrayList tree= new ArrayList();
        tree.add("杨树");
        tree.add("桃树");
        tree.add("柳树");
        tree.add("梨树");
        ListIterator li=tree.listIterator();
        while (li.hasNext())
        {
            System.out.println(li.next());
        }
        while (li.hasPrevious())
        {
            System.out.println(li.previous());
        }

    }
}

ArrayList类线程不同步

Vector 类线程同步

LinkedList类插入元素速度特别快

Set集合类似一个“罐子”元素是无序的。

Set集合没有提供额外的方法与Collection一样。

HashSet类

HashSet是不同步的

HashSet判断两个元素相等的标准是：两个对象通过equals方法比较相等，并且两个对象hasCode()方法返回值也相等。

 1 import java.util.*;
 2 class HashSetDemo
 3 {
 4     public static void main(String[] args) 
 5     {
 6         HashSet hs=new HashSet();
 7         hs.add(new A());
 8         hs.add(new A());
 9         hs.add(new B());
10         hs.add(new B());
11         hs.add(new C());
12         hs.add(new C());
13         System.out.println(hs);
14         //运行结构[C@16e1fb1, A@1, A@1, B@2, C@e2cb55]
15     }
16 }
17 class A
18 {
19     public int hashCode()
20     {
21         return 1;
22     }
23 }
24 class B
25 {
26     public int hashCode()
27     {
28         return 2;
29     }
30     public boolean equals(Object obj)
31     {
32         return true;
33     }
34 }
35 class C
36 {
37     public boolean equals(Object obj)
38     {
39         return true;
40     }
41 }

当hashCode()返回值不同不调用equals方法只有hashCode()返回值相同时调用equals方法

 1 import java.util.*;
 2 class  HashSetDemo2
 3 {
 4     public static void main(String[] args) 
 5     {
 6         HashSet hs=new HashSet();
 7         hs.add(new Student(15,"张三"));
 8         hs.add(new Student(16,"李四"));
 9         hs.add(new Student(16,"李四"));
10         hs.add(new Student(17,"王五"));
11         Iterator it=hs.iterator();
12         while (it.hasNext())
13         {
14             Student stu=(Student)it.next();
15             System.out.println(stu.getAge()+","+stu.getName());
16         }
17     }
18 }
19 /*
20 调用hasCode()
21 调用hasCode()
22 调用hasCode()
23 调用equals方法
24 调用hasCode()
25 17,王五
26 15,张三
27 16,李四
28 */
29 class Student
30 {
31     private int age;
32     private String name;
33     Student(int age,String name)
34     {
35         this.age=age;
36         this.name=name;
37     }
38     public int getAge()
39     {
40         return age;
41     }
42     public String getName()
43     {
44         return name;
45     }
46     public int hashCode()
47     {
48         System.out.println("调用hasCode()");
49         return name.hashCode()+age*13;
50     }
51     public  boolean equals(Object obj)
52     {
53         System.out.println("调用equals方法");
54         if(!(obj instanceof Student))
55             throw new ClassCastException("类型转换异常");
56         Student s=(Student)obj;
57         return this.name.equals(s.name)&&this.age==s.age;
58     }
59 }

TreeSet类

TreeSet可以使集合处于排序状态

 1 import java.util.*;
 2 class  TreeSetDemo
 3 {
 4     public static void main(String[] args) 
 5     {
 6         TreeSet ts=new TreeSet();
 7         ts.add(new Student(19,"张三"));
 8         ts.add(new Student(17,"李四"));
 9         ts.add(new Student(23,"王五"));
10         ts.add(new Student(19,"赵六"));
11         Iterator it=ts.iterator();
12         while (it.hasNext())
13         {
14             Student stu=(Student)it.next();
15             System.out.println(stu.getAge()+","+stu.getName());
16 
17         }
18     }
19 }
20 class Student implements Comparable 
21 {
22     public int age;
23     public String name;
24     Student(int age,String name)
25     {
26         this.age=age;
27         this.name=name;
28     }
29     public int getAge()
30     {
31         return age;
32     }
33     public String getName()
34     {
35         return name;
36     }
37     public int compareTo(Object obj)
38     {
39         if(!(obj instanceof Student))
40             throw new RuntimeException("不是学生！");
41         Student s=(Student)obj;
42         if(this.age>s.age)
43             return 1;
44         if(this.age==s.age)
45             return this.name.compareTo(s.name);
46         return -1;
47     }
48 }

Comparator接口

 1 import java.util.*;
 2 class  TreeSetDemo2
 3 {
 4     public static void main(String[] args) 
 5     {
 6         TreeSet ts=new TreeSet(new MyComp());
 7         ts.add(new Student(19,"zhangsan"));
 8         ts.add(new Student(17,"lisi"));
 9         ts.add(new Student(23,"wangwu"));
10         ts.add(new Student(19,"zhaoliu"));
11         ts.add(new Student(21,"zhaoliu"));
12         Iterator it=ts.iterator();
13         while (it.hasNext())
14         {
15             Student stu=(Student)it.next();
16             System.out.println(stu.getAge()+","+stu.getName());
17 
18         }
19     }
20 }
21 class Student implements Comparable 
22 {
23     public int age;
24     public String name;
25     Student(int age,String name)
26     {
27         this.age=age;
28         this.name=name;
29     }
30     public int getAge()
31     {
32         return age;
33     }
34     public String getName()
35     {
36         return name;
37     }
38     public int compareTo(Object obj)
39     {
40         if(!(obj instanceof Student))
41             throw new RuntimeException("不是学生!");
42         Student s=(Student)obj;
43         if(this.age>s.age)
44             return 1;
45         if(this.age==s.age)
46             return this.name.compareTo(s.name);
47         return -1;
48     }
49 }
50 class MyComp implements Comparator
51 {
52     public int compare(Object o1,Object o2)
53     {
54         if(!((o1 instanceof Student)&&(o2 instanceof Student)))
55             throw new RuntimeException("不是学生!");
56         Student s1=(Student)o1;
57         Student s2=(Student)o2;
58         int num=s1.getName().compareTo(s2.getName());
59         if(num==0)
60             return new Integer(s1.getAge()).compareTo(new Integer(s2.getAge()));
61         return num;
62     }
63 }

练习：字符串按照长度排序

 1 import java.util.*;
 2 class  TreeSetDemo3
 3 {
 4     public static void main(String[] args) 
 5     {
 6         TreeSet ts=new TreeSet(new MyComp());
 7         ts.add("abc92");
 8         ts.add("dhf");
 9         ts.add("kdsjfkjdks");
10         ts.add("kf");
11         Iterator it=ts.iterator();
12         while (it.hasNext())
13         {
14             System.out.println(it.next());
15 
16         }
17     }
18 }
19 class MyComp implements Comparator
20 { 
21     public int compare(Object o1,Object o2)
22     {
23         String s1=(String)o1;
24         String s2=(String)o2;
25         return new Integer(s1.length()).compareTo(new Integer(s2.length()));
26 
27     }
28 
29 }

posted on 2012-06-04 22:34 Lincon Ma 阅读(242) 评论(0) 编辑收藏举报