集合（二）

set接口

• set接口存放一组唯一无序的对象
• hash Set是set接口常用是想类
• set接口不存在get（)方法

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• 程序类：public class Topic {
  private int id;
  private String title;
  public int getId() {
  return id;
  }
  public void setId(int id) {
  this.id = id;
  }
  public String getTitle() {
  return title;
  }
  public void setTitle(String title) {
  this.title = title;
  }

  public Topic(int id, String title) {
  super();
  this.id = id;
  this.title = title;
  }
  public Topic() {
  super();
  }
  }

• import java.util.HashSet;
  import java.util.Iterator;

public class SetDemo {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    HashSet<Topic> topics=new HashSet<Topic>();
    Topic topic1=new Topic(1,"七夕快乐吗？");
    Topic topic2=new Topic(2,"上课快乐吗？");
    Topic topic3=new Topic(3,"写代码快乐吗？");

    topics.add(topic1);
    topics.add(topic2);
    topics.add(topic3);
    //添加多余的被筛掉
    topics.add(topic1);
    topics.add(topic2);
    topics.add(topic3);

    /*topic1=new Topic(1,"七夕不快乐");*/
    //根据对象的内存地址来判断的
    topic1.setId(1);
    topic1.setTitle("我不快乐");
    topics.add(topic1);


    Iterator<Topic> it=topics.iterator();
    while(it.hasNext()) {
        System.out.println(it.next().getTitle());
    }
}

}

hashMap

• 建立类：public class Goods {
  private int id;
  private String name;
  private float price;
  public Goods(int id, String name, float price) {
  super();
  this.id = id;
  this.name = name;
  this.price = price;
  }
  public Goods() {
  super();
  }
  public int getId() {
  return id;
  }
  public void setId(int id) {
  this.id = id;
  }
  public String getName() {
  return name;
  }
  public void setName(String name) {
  this.name = name;
  }
  public float getPrice() {
  return price;
  }
  public void setPrice(float price) {
  this.price = price;
  }
  public Integer get(Object good) {
  // TODO Auto-generated method stub
  return null;
  }

}

• import java.util.HashMap;
  import java.util.Iterator;

public class ShopCar {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    //键值对集合
    //遍历键就可以了
    //但是键是set不准重合  所以不能重合
    HashMap<Goods, Integer> shopcar=new HashMap<Goods,Integer>();



    Goods good1=new Goods(1,"心形石头",200);
    Goods good2=new Goods(2,"巧克力",199);
    Goods good3=new Goods(3,"狗粮",10);

    //hashmap添加元素用put
    shopcar.put(good1, 10);
    shopcar.put(good2, 2);
    shopcar.put(good3, 21);

    //无序集合遍历的数组是随机出现的
    for(Goods good:shopcar.keySet()) {
        System.out.println(good.getName()+"\t"+good.getPrice()+"\t"+shopcar.get(good).intValue());

    }

    /*Iterator<Goods> it=shopcar.keySet().iterator();
    while (it.hasNext()) {
        Goods it1=it.next();
        System.out.println(it1.getName()+"\t"+it1.getPrice()+"\t"+shopcar.get(it1).intValue()); 

    }*/



    System.out.println("**************delete*****************");
    shopcar.remove(good1);
    Iterator<Goods> it2=shopcar.keySet().iterator();
    while (it2.hasNext()) {
        Goods it1=it2.next();
        System.out.println(it1.getName()+"\t"+it1.getPrice()+"\t"+shopcar.get(it1).intValue()); 

    }

}

}

算法collections工具类

• 实例：import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Iterator;

public class CollationsDemo {

public static void main(String[] args) {
    ArrayList<Integer> list1=new ArrayList<Integer>();

    list1.add(100);
    list1.add(78);
    list1.add(87);
    list1.add(1);

    for (Integer n:list1) {

        System.out.println(n);

    }

    System.out.println("**************sorted（排序）*************");
    Collections.sort(list1);
    for (Integer n:list1) {

        System.out.println(n);

    }


    System.out.println("**************reverse(翻转)*************");

    Collections.reverse(list1);
    /*for (Integer n:list1) {

        System.out.println(n);

    }*/


    Iterator<Integer> iterator=list1.iterator();
    while(iterator.hasNext()) {
        System.out.println(iterator.next());
    }

    System.out.println("**************字符串集合*************");

    ArrayList<String> stringset=new ArrayList<String>();

    stringset.add("qb");
    stringset.add("Qb");
    stringset.add("qB");
    stringset.add("QB");

    System.out.println("**************没有排序*************");
    Iterator<String> iterator1=stringset.iterator();
    while(iterator1.hasNext()) {
        System.out.println(iterator1.next());
    }

    System.out.println("**************排序后*************");
    Collections.sort(stringset);

    Iterator<String> iterator2=stringset.iterator();
    while(iterator2.hasNext()) {
        System.out.println(iterator2.next());
    }
}

}