java 对list进行排序
前提:
list中的元素是自定义对象,如何根据对象的元素进行排序呢?
比如List<Student>students 是一个list,每个元素都是Student对象,Student对象中有成员变量name,age,等,
那么我想根据age来排序,如何实现呢?
1,使用Comparator 接口
Student类 结构如下:( 省略getter,setter方法 )
public class Student { /*** * 姓名 */ private String name; private int age; private String address; /*** * 考试得分 */ private int score; //省略getter,setter方法 @Override public String toString() { return "Student [name=" + name + ", age=" + age + ", score=" + score + "]"; } }
测试方法:
@Test public void test_ListComparator(){ List<Student>students=new ArrayList<Student>(); Student stu=null; stu=new Student(); stu.setName("whuang"); stu.setAge(12); stu.setScore(80); students.add(stu); stu=new Student(); stu.setName("rong"); stu.setAge(11); stu.setScore(90); students.add(stu); stu=new Student(); stu.setName("zhu"); stu.setAge(15); stu.setScore(100); students.add(stu); Collections.sort(students,new SystemHWUtil. ListComparator(true,"age")); System.out.println(students); }
运行结果:
[Student [name=rong, age=11, score=90], Student [name=whuang, age=12, score=80], Student [name=zhu, age=15, score=100]]
核心类:
public static class ListComparator implements Comparator{ /*** * 是否转化为Int之后再比较 */ private boolean isConvertInteger; /*** * 对哪个列进行排序 */ private String comparedProperty; public ListComparator(boolean isConvertInteger,String comparedProperty) { super(); this.isConvertInteger = isConvertInteger; this.comparedProperty=comparedProperty; } public int compare(Object o1, Object o2) { if(null!=o1&&null!=o2) { try { Object obj1=ReflectHWUtils.getObjectValue(o1, comparedProperty); Object obj2=ReflectHWUtils.getObjectValue(o2, comparedProperty); if(isConvertInteger){ int num1; int num2; if(obj1 instanceof Integer){ num1=(Integer)obj1; num2=(Integer)obj2; }else{ num1=Integer.parseInt(obj1.toString()); num2=Integer.parseInt(obj2.toString()); } if(num1>num2){ return 1; }else if(num1<num2){ return -1; }else{ return 0; } }else{ return obj1.toString().compareTo(obj2.toString()); } } catch (SecurityException e) { e.printStackTrace(); } catch (NoSuchFieldException e) { e.printStackTrace(); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } } return 0/*等于*/; } }
2,可以指定是升序还是降序
实例:
@Test public void test_ListComparator(){ List<Student>students=new ArrayList<Student>(); Student stu=null; stu=new Student(); stu.setName("whuang"); stu.setAge(12); stu.setScore(80); students.add(stu); stu=new Student(); stu.setName("rong"); stu.setAge(11); stu.setScore(90); students.add(stu); stu=new Student(); stu.setName("zhu"); stu.setAge(15); stu.setScore(100); students.add(stu); SortList<Student> sortList = new SortList<Student>(); sortList.Sort(students, "getAge", "asc"); System.out.println(students); }
注意:sortList.Sort 的 第二个参数是方法名 ,不是成员变量名.
核心代码
package com.common.util; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.Collections; import java.util.Comparator; import java.util.List; public class SortList<E> { public void Sort(List<E> list, final String method, final String sort) { Collections.sort(list, new Comparator() { public int compare(Object a, Object b) { int ret = 0; try { Method m1 = ((E) a).getClass().getMethod(method, null); Method m2 = ((E) b).getClass().getMethod(method, null); if (sort != null && "desc".equals(sort))// 倒序 ret = m2.invoke(((E) b), null).toString() .compareTo(m1.invoke(((E) a), null).toString()); else // 正序 ret = m1.invoke(((E) a), null).toString() .compareTo(m2.invoke(((E) b), null).toString()); } catch (NoSuchMethodException ne) { System.out.println(ne); } catch (IllegalAccessException ie) { System.out.println(ie); } catch (InvocationTargetException it) { System.out.println(it); } return ret; } }); } }
参考:
http://hw1287789687.iteye.com/blog/2223537
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666
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文章和留言都翻到11页了 没有OOM
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朋友，翻页到11页，及以后，会出现OOM，无法访问
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版本号是多少，你可以下载哪个代码仓库，jdk选1.8 直接跑就行
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