JAVA List合并集合

import java.util.ArrayList;
import java.util.List;

public class test {
      public static void main(String[] args) throws Exception {
          /*测试合并两个类型相同的list*/
          List<String> list1 = new ArrayList<String>();
          List<String> list2 = new ArrayList<String>();
          //给list1赋值
          list1.add("测");
          list1.add("试");
          list1.add("一");
          list1.add("下");
          //给list2赋值
          list2.add("合");
          list2.add("并");
          list2.add("列");
          list2.add("表");
          //将list1.list2合并
          list1.addAll(list2);
          //循环输出list1 看看结果
          for (String s : list1) {
              System.out.print(s);
          }
      }
}

 

 

需求：两个字符串合并（如果想去重复，参考下一篇--数组去重复及记录重复个数）
//方法一 Arrays类
    String[] a = {"A","B","C"};
    String[] b = {"D","E"};
    // List<String> list = Arrays.asList(a);   --OK
    // List<String> list = Arrays.asList("A","B","C");  --OK
    // list.add("F");  --UnsupportedOperationException
    // list.remove("A"); --UnsupportedOperationException
    // list.set(1,"javaee");--OK (因为是把数组转为集合，其本质还是数组，数组长度固定不变，但内容可以改变)
    // 结论：虽然可以把数组转为集合，但是集合长度不能改变

    List list = new ArrayList(Arrays.asList(a));
    list.addAll(Arrays.asList(b));
    String[] str = new String[list.size()];
    list.toArray(str);    
    for(int x=0;x<str.length;x++){
        System.out.print(str[x] + " ");
    }
//方法二  循环遍历
// 两个数组合并
    String[] str1 = {"Hello","world","java"};
    String[] str2 = {"Veriable","syntax","interator"};
    String[] newStr = new String[str1.length+str2.length];
    //newStr = str1;数组是引用类型
    for(int x=0;x<str1.length;x++){
        newStr[x] = str1[x];
    }        
    for(int y=0;y<str2.length;y++){
        newStr[str1.length+y]=str2[y];
    }
    for(int y=0;y<newStr.length;y++){
        System.out.println(newStr[y] + " ");
    }
// 方法三
    String[] str1 = {"Hello","world","java"};
    String[] str2 = {"Veriable","syntax","interator"};
    int str1Length = str1.length;
    int str2length = str2.length;
        
    str1 = Arrays.copyOf(str1, str1Length+str2length);//数组扩容
    System.arraycopy(str2, 0, str1, str1Length, str2length);
    System.out.println(Arrays.toString(str1));

 

java求两个集合的交集和并集

        java如何求两个集合的交集和并集呢？？其实java的API中已经封装了方法。今天写个简单的例子测试一下：（例子中以java.util.LinkedList为例）

        求连个集合的交集：

import java.util.ArrayList;
import java.util.List;
public class TestCollection {
    public static void main(String[] args) {
        List<String> strList = new ArrayList<String>();
        List<String> strList2 = new ArrayList<String>();
        for(int i = 0; i < 10; i ++) {
            strList.add("aaa>>" + i);
            strList2.add("aaa>>" + (10 - i));
        }
         
        //求出交集
        strList2.retainAll(strList);
        System.out.println("交集大小：" + strList2.size());
         
        for(int i = 0; i < strList2.size(); i++) {
            System.out.println(strList2.get(i));
        }       
    }
}




求两个集合的并集：
import java.util.ArrayList;
import java.util.List;
public class TestCollection {
    public static void main(String[] args) {
        List<String> strList = new ArrayList<String>();
        List<String> strList2 = new ArrayList<String>();
        for(int i = 0; i < 10; i ++) {
            strList.add("aaa>>" + i);
            strList2.add("aaa>>" + (10 - i));
        }
        //求出并集
        strList2.removeAll(strList);
        strList2.addAll(strList);
        System.out.println("并集大小：" + strList2.size());      
         
        for(int i = 0; i < strList2.size(); i++) {
            System.out.println(strList2.get(i));
        }       
    }
}

java 使用map返回多个对象组装

 Object json=JSONObject.fromObject("{}");
List<Object> list = new ArrayList<Object>();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");
list.add("6");
List<Object> result = new ArrayList<Object>();
Map<String, Object> map = new HashMap<String, Object>();
for(Object str :list){
    map.put("name", str);
    map.put("age", str);
    result.add(map);
}
JSONArray arr=JSONArray.fromObject(result);
if(arr!=null){
    json=arr;
}
System.out.println(arr);
　　输出值格式为：[{"age":"6","name":"6"},{"age":"6","name":"6"},{"age":"6","name":"6"},{"age":"6","name":"6"},{"age":"6","name":"6"},{"age":"6","name":"6"}]