黑马程序员_集合的小练习

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1. 使用LinkedList模拟一个堆栈或者队列数据结构。

import java.util.*;class Queue{private LinkedList link;Queue(){link = new LinkedList();}public void myAdd(Object obj){link.addFirst(obj);}public Object myGet(){return link.removeFirst();}public boolean isNull(){return link.isEmpty();}}class  LinkedListTest{public static void main(String[] args) {Queue q = new Queue();q.myAdd("java01");q.myAdd("java02");q.myAdd("java03");q.myAdd("java04");while(!q.isNull()){System.out.println(q.myGet());}}}

2. 去除ArrayList集合中的重复元素。

import java.util.*;class ArrayListTest {public static void sop(Object obj){System.out.println(obj);}public static void main(String[] args) {ArrayList al = new ArrayList();al.add("java01");al.add("java02");al.add("java01");al.add("java02");al.add("java01");//al.add("java03");/*在迭代时循环中next调用一次，就要hasNext判断一次。Iterator it = al.iterator();while(it.hasNext()){sop(it.next()+"...."+it.next());}*//**/sop(al);al = singleElement(al);sop(al);}public static ArrayList singleElement(ArrayList al){//定义一个临时容器。ArrayList newAl = new ArrayList();Iterator it = al.iterator();while(it.hasNext()){Object obj = it.next();if(!newAl.contains(obj))newAl.add(obj);}return newAl;}}

3. 将自定义对象作为元素存到ArrayList集合中，并去除重复元素。
比如：存人对象，同姓名同年龄，视为同一个人。为重复元素。

/*将自定义对象作为元素存到ArrayList集合中，并去除重复元素。比如：存人对象，同姓名同年龄，视为同一个人。为重复元素。思路：1. 对人描述，将数据封转进人对象。2. 定义容器，将人存入。3. 取出。List集合判断元素是否相同，依据的是元素的equals方法。*/import java.util.*;class Person{private String name;private int age;Person(String name , int age){this.name = name;this.age = age;}public String getName(){return name;}public int getAge(){return age;}public boolean equals(Object obj){if(!(obj instanceof Person))return false;Person p = (Person)obj;System.out.println(this.name+"...."+p.name);return this.name.equals(p.name) && this.age == p.age;}}class  ArrayListTest2{public static void sop(Object obj){System.out.println(obj);}public static void main(String[] args) {ArrayList al = new ArrayList();al.add(new Person("lisi01",30));//存储的是地址的引用al.add(new Person("lisi02",32));al.add(new Person("lisi02",32));al.add(new Person("lisi03",33));al.add(new Person("lisi04",35));al.add(new Person("lisi04",35));al = singleElement(al);Iterator it = al.iterator();while (it.hasNext()){Person p = (Person)it.next();sop(p.getName()+"::"+p.getAge());}}public static ArrayList singleElement(ArrayList al){//定义一个临时容器ArrayList newAl = new ArrayList();Iterator it = al.iterator();while (it.hasNext()){Object obj = it.next();if(!newAl.contains(obj))newAl.add(obj);}return newAl;}}

 4. 往hashSet集合中存入自定对象
姓名和年龄相同为同一个人，重复元素。

import java.util.*;class HashSetTest {public static void sop(Object obj){System.out.println(obj);}public static void main(String[] args) {HashSet hs = new HashSet();hs.add(new Person("a1",11));hs.add(new Person("a2",12));hs.add(new Person("a3",13));//hs.add(new Person("a2",12));//hs.add(new Person("a4",14));//sop("a1:"+hs.contains(new Person("a2",12)));//hs.remove(new Person("a4",13));Iterator it = hs.iterator();while(it.hasNext()){Person p = (Person)it.next();sop(p.getName()+"::"+p.getAge());}}}class Person{private String name;private int age;Person(String name,int age){this.name = name;this.age = age;}public int hashCode(){System.out.println(this.name+"....hashCode");return name.hashCode()+age*37;}public boolean equals(Object obj){if(!(obj instanceof Person))return false;Person p = (Person)obj;System.out.println(this.name+"...equals.."+p.name);return this.name.equals(p.name) && this.age == p.age;}public String getName(){return name;}public int getAge(){return age;}}

5. 往TreeSet集合中存储自定义对象学生。
想按照学生的年龄进行排序。

/*需求：往TreeSet集合中存储自定义对象学生。想按照学生的年龄进行排序。思路：实现Comparable，覆写compareTo方法。判断主要条件及次要条件。*/import java.util.*;class TreeSetDemo{public static void main(String[] args){TreeSet ts = new TreeSet();ts.add(new Student("lisi02",22));ts.add(new Student("lisi007",20));ts.add(new Student("lisi09",19));    ts.add(new Student("lisi01",40));ts.add(new Student("lisi08",19));for (Iterator it = ts.iterator(); it.hasNext(); ){Student stu = (Student)it.next();System.out.println(stu.getName()+"..."+stu.getAge());}}}class Student implements Comparable//该接口强制让学生具备比较性{private String name;private int age;Student(String name,int age){this.name = name;this.age = age;}//覆盖Comparable中的compareTo方法public int compareTo(Object obj){//先判断obj是不是学生的一个实例，如果不是，抛出一个异常if(!(obj instanceof Student))throw new RuntimeException("不是学生对象");//强制转换Student s = (Student)obj;System.out.println(this.name+"....compareto...."+s.name);//当此对象大于指定对象，返回正数if(this.age>s.age)return 1;//排序时，当主要条件相同时，还要判断一下次要条件。if(this.age==s.age){return this.name.compareTo(s.name);}return -1;}public String getName(){return name;}public int getAge(){return age;}}

 6. 照字符串长度排序。

/*练习：按照字符串长度排序思路：字符串本身具备比较性，但是它的比较方式不是所需要的。这是就只能使用比较器。步骤：用一个类去实现接口。比较主要条件和次要条件。*/import java.util.*;class TreeSetTest{public static void main(String[] args){TreeSet ts = new TreeSet(new StrLenComparator());ts.add("abcd");ts.add("cc");ts.add("cba");ts.add("aaa");ts.add("z");ts.add("hahaha");for (Iterator it = ts.iterator(); it.hasNext(); ){System.out.println(it.next());}}}class StrLenComparator implements Comparator{//覆写Comparator中的compare方法public int compare(Object o1,Object o2){//强转String s1 = (String)o1;String s2 = (String)o2;int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));if(num==0)return s1.compareTo(s2);return num;}}

 

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