Android List(集合)中的对象以某一个字段排序案例

在Android开发中，有时我们需要对一个对象的集合按照某一个字段进行排序，

Bean

public class Student {
private int studentId;
private String studentName;
private int age;
public Student(int studentId , String studentName, int age){
 this.studentId=studentId;
 this.studentName=studentName;
 this.age=age;
}
public int getStudentId() {
 return studentId;
}
public void setStudentId(int studentId) {
 this.studentId = studentId;
}
public String getStudentName() {
 return studentName;
}
public void setStudentName(String studentName) {
 this.studentName = studentName;
}
public int getAge() {
 return age;
}
public void setAge(int age) {
 this.age = age;
}

}

实现排序

实现排序比较类 Comparator ，里面实现排序规则。

public class test {

/**
 * @param args
 */
public static void main(String[] args) {
  Student stu1 = new Student (1,"zhangsan",28);
  Student stu2 = new Student (2,"zhagnsan",19);
  Student stu3 = new Student (3,"wangwu",19);
  Student stu4 = new Student (4,"wangwu",19);
  Student stu5 = new Student (5,"zhaoliu",18);

ArrayList<Student> list = new ArrayList<Student>();
  list.add(stu1);
  list.add(stu2);
  list.add(stu3);
  list.add(stu4);
  list.add(stu5);
//排序规则，这里是以年龄先排序，如果年龄相同
 Comparator<Student> comparator = new Comparator<Student>() {
  public int compare(Student s1, Student s2) {
   // 先排年龄
   if (s1.getAge() != s2.getAge()) {
    return s1.getAge() - s2.getAge();
   } else if (!s1.getStudentName().equals(s2.getStudentName())) {
    // 年龄相同则按姓名排序
    return s1.getStudentName().compareTo(s2.getStudentName());
   } else {
    // 姓名也相同则按学号排序
    return s1.getStudentId() - s2.getStudentId();
   }
  }
 };

//这里就会自动根据规则进行排序
  Collections.sort(list,comparator);
  for(int i=0;i<list.size();i++){
   Student stu=list.get(i);
   System.out.println("年龄:"+stu.getAge()+" 姓名:"+stu.getStudentName()+" 学号:"+stu.getStudentId());
  }

}

}

排序结果

结果：

年龄:18 姓名:zhaoliu 学号:5

年龄:19 姓名:wangwu 学号:3

年龄:19 姓名:wangwu 学号:4

年龄:19 姓名:zhagnsan 学号:2

年龄:28 姓名:zhangsan 学号:1

也可以想下面这样写：

Collections.sort(list, new Comparator<GoodsBean>() {
  @Override
  public int compare(GoodsBean bean1, GoodsBean bean2) {

if (Integer.valueOf(bean1.getScore()).compareTo(Integer.valueOf(bean2.getScore())) == 0) {
    return Integer.valueOf(bean1.getRecommend_num()).compareTo(Integer.valueOf(bean2.getRecommend_num()));
   } else {
    return Integer.valueOf(bean1.getScore()).compareTo(Integer.valueOf(bean2.getScore()));
   }
  }
 });

这样就可以对一个集合中的数据各种排序了。

补充知识：java利用映射表名称反射创建实体类并赋属性值

1.hibernate中首先进行初始化，将对应的表名和类名以键值对的方式存放到map中

private Map<String, String> mappings;//全局变量

/**
* 根据数据库表名获取实体类
*/
public void initMappings() {
if (mappings == null) {
mappings = new HashMap<String, String>();
SessionFactory factory = this.getSessionFactory();
Map metaMap = factory.getAllClassMetadata();
for (String key : (Set<String>) metaMap.keySet()) {
AbstractEntityPersister classMetadata = (AbstractEntityPersister) metaMap.get(key);
String tableName = classMetadata.getTableName().toLowerCase();
int index = tableName.indexOf(".");
if (index >= 0) {
tableName = tableName.substring(index + 1);
}
String className = classMetadata.getEntityMetamodel().getName();
mappings.put(tableName, className);
}
}
}

2.调用方法，传入表名得到对应的实体类名

public String getEntityNameByTableName(String tableName) {
initMappings();
return mappings.get(tableName);
}

3.根据实体类名创建实体类

/**
*listobj:要赋的属性值集合，顺序要和实体类属性顺序一致

*/

public Object getByReflect(String tableName, List listobj)throws Exception {

Class<?> model = Class.forName(tableName);
Object object = new Object();

if (model != null) {
 Field[] field = model.getDeclaredFields();
String[] modelName = new String[field.length];
 String[] modelType = new String[field.length];

object = model.newInstance();
Method m = null;

for (int i = 1; i <field.length ; i++) {
 String name = field[i].getName();
 Object value = null;
name = name.substring(0, 1).toUpperCase() + name.substring(1);
 String type = field[i].getGenericType().toString();
  if (type.equals("class java.lang.String")) {
 m = model.getDeclaredMethod("set" + name, String.class);

if(listobj.get(i - 1) instanceof Double){
  Double d=(Double) listobj.get(i-1);
  value=String.valueOf(d);

}else{
  value =(String)listobj.get(i - 1);
 }
 }
 if (type.equals("class java.lang.Integer")) {
 m = model.getDeclaredMethod("set" + name, Integer.class);
 Double d = (Double) listobj.get(i - 1);
 value = Integer.valueOf(d.intValue());
 }
 if (type.equals("class java.lang.Short")) {
 m = model.getDeclaredMethod("set" + name, Short.class);
 value = (Short) listobj.get(i - 1);
 }
 if (type.equals("class java.lang.Float")) {
 m = model.getDeclaredMethod("set" + name, Float.class);
 value = (Float) listobj.get(i - 1);
 }
 if (type.equals("class java.lang.Double")) {
 m = model.getDeclaredMethod("set" + name, Double.class);
 value = (Double) listobj.get(i - 1);
 }
 if (type.equals("class java.lang.Boolean")) {
 m = model.getDeclaredMethod("set" + name, Boolean.class);
 value = (Boolean) listobj.get(i - 1);
 }
  if (m != null) {
 m.invoke(object, value);
}
 }

}
 return object;
}

来源：https://blog.csdn.net/Kenway090704/article/details/78408529