Java的map和list学习 （1）

  • Z时代
  • 2024-01-10
  • 分类：综合

java

Java中List集合去除重复数据的方法

原链接地址

1.通过HashSet除重复元素

public static List removeDuplicate(List list) {   
    HashSet h = new HashSet(list);   
    list.clear();   
    list.addAll(h);   
    return list;   
}

2.把list里的对象遍历一遍，用list.contain()，如果不存在就放入到另外一个list集合中`

public static List removeDuplicate(List list){  
        List listTemp = new ArrayList();  
        for(int i=0;i<list.size();i++){  
            if(!listTemp.contains(list.get(i))){  
                listTemp.add(list.get(i));  
            }  
        }  
        return listTemp;  
    }

3.删除ArrayList中重复元素，保持顺序

// 删除ArrayList中重复元素，保持顺序     
 public static void removeDuplicateWithOrder(List list) {    
    Set set = new HashSet();    
     List newList = new ArrayList();    
   for (Iterator iter = list.iterator(); iter.hasNext();) {    
         Object element = iter.next();    
         if (set.add(element))    
            newList.add(element);    
      }     
     list.clear();    
     list.addAll(newList);    
    System.out.println( " remove duplicate " + list);    
 }

Map<\string，string>的遍历的四种方法

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.HashSet;
import java.util.Set;
import java.util.TreeMap;
public class NumCounter {
     public static void main(String[] args) throws Exception {
      Map<String, String> map = new HashMap<>();  
      map.put("key1","value1");  
      map.put("key2", "value2");  
      map.put("key3", "value3");  
      //第一种：普遍使用，二次取值
      System.out.println("通过Map.keySet遍历key和value：");
      for (String key : map.keySet()) {  
       System.out.println("key= "+ key + " and value= " + map.get(key));  
      }  
      //第二种  
      System.out.println("通过Map.entrySet使用iterator遍历key和value：");  
      Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();  
      while (it.hasNext()) {  
       Map.Entry<String, String> entry = it.next();  
       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  
      }  
      //第三种：推荐，尤其是容量大时</span>  
      System.out.println("通过Map.entrySet遍历key和value");  
      for (Map.Entry<String, String> entry : map.entrySet()) {  
       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  
      }  
      //第四种  
      System.out.println("通过Map.values()遍历所有的value，但不能遍历key");  
      for (String v : map.values()) {  
       System.out.println("value= " + v);  
      }  
}
}

JAVA中Map的使用

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class NumCounter {
    public static void main(String[] args) {
        Map<String , Student> stu = new HashMap<String, Student>();
        //添加元素
        stu.put("0001", new Student("sunming1"));
        stu.put("0002", new Student("sunming2"));
        stu.put("0003", new Student("sunmnig3"));
        System.out.println(stu);
        System.out.println("-------------------------");
        //删除元素
        stu.remove("0001");
        System.out.println(stu);
        System.out.println("-------------------------");
        //更新元素
        stu.put("0002", new Student("sunmingUpdate"));
        System.out.println(stu);
        System.out.println("-------------------------");
        //查询元素
        System.out.println(stu.get("0003"));
        System.out.println("-------------------------");
        //获取所有的key和value
        for(Map.Entry<String, Student> entry : stu.entrySet()){
            System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
        }
        System.out.println("-------------------------");
        //获取所有的key
        Set<String> keys = stu.keySet();
        for(String key: keys){
            System.out.println(key);
        }
        System.out.println("-------------------------");
        //获取所有的value
        Collection<Student> values = stu.values();
        for(Student value: values){
            System.out.println(value);
        }
    }
}

/**
 * Created by SunMing on 2016/9/18.
 */
public class Student {
    private String id;
    private String name;
    public Student(String strName) {
        name = strName;
        id = "00";
    }
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String toString() {
        return id + " " + name + ", ";
    }
}

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