Java中List集合排序的方法 比較器的使用 根據學生對象數序 語文 英語成績總和進行sort排序
阿新 • • 發佈：2018-01-13
private system.in set swift ringbuf 直觀 turn @override encoding
package com.swift; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; import java.util.Scanner; public class Test2_ObjectIO { @SuppressWarnings("unchecked") public static void main(String[] args) { /* * 第2題: 有五個學生，每個學生有3門課（語文、數學、英語）的成績，寫一個程序接收從鍵盤輸入學生的信息， * 輸入格式為：name,30,30,30（姓名，三門課成績），然後把輸入的學生信息按總分從高到低的順序寫入到一個名稱"stu.txt"文件中。 * 要求：stu.txt文件的格式要比較直觀，打開這個文件，就可以很清楚的看到學生的信息。*/ List<Student> list = new ArrayList<Student>(); Scanner scan = new Scanner(System.in); for (int i = 1; i <=5; i++) { System.out.println("請輸入第"+i+"學生信息：格式為 name 60 60 60"); String name = scan.next(); Float yuwen = scan.nextFloat(); Float shuxue= scan.nextFloat(); Float yingyu = scan.nextFloat(); Student stu = new Student(name, yuwen, shuxue, yingyu); list.add(stu); } for(Student stu:list) { System.out.println(stu.toString()); } Collections.sort(list,new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { float num=(o2.getShuxue()+o2.getYingyu()+o2.getYuwen())-(o1.getShuxue()+o1.getYingyu()+o1.getYuwen()); int i=(int) num; return i; } }); for(Student stu:list) { System.out.println(stu.toString()); } } } class Student { private String name; private float yuwen; private float shuxue; private float yingyu; public String getName() { return name; } public void setName(String name) { this.name = name; } public float getYuwen() { return yuwen; } public void setYuwen(float yuwen) { this.yuwen = yuwen; } public float getShuxue() { return shuxue; } public void setShuxue(float shuxue) { this.shuxue = shuxue; } public float getYingyu() { return yingyu; } public void setYingyu(float yingyu) { this.yingyu = yingyu; } public Student(String name, float yuwen, float shuxue, float yingyu) { super(); this.name = name; this.yuwen = yuwen; this.shuxue = shuxue; this.yingyu = yingyu; } public Student() { super(); } @Override public String toString() { return "Student [name=" + name + ", yuwen=" + yuwen + ", shuxue=" + shuxue + ", yingyu=" + yingyu + "]"; } }
比較器就是個匿名內部類，Collections.sort(list,Comparator<Student>(){});
然後實現其中的compare方法，返回一個int類型的值，正數 負數 0分別代表大於小於等於
增加IO流的內容代碼如下；
package com.swift; import java.io.BufferedWriter; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStreamWriter; import java.io.UnsupportedEncodingException; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; import java.util.Scanner; public class Test2_ObjectIO { @SuppressWarnings("unchecked") public static void main(String[] args) { /* * 第2題: 有五個學生，每個學生有3門課（語文、數學、英語）的成績，寫一個程序接收從鍵盤輸入學生的信息， * 輸入格式為：name,30,30,30（姓名，三門課成績），然後把輸入的學生信息按總分從高到低的順序寫入到一個名稱"stu.txt"文件中。 * 要求：stu.txt文件的格式要比較直觀，打開這個文件，就可以很清楚的看到學生的信息。 */ List<Student> list = initiateList(); for(Student stu:list) { System.out.println(stu.toString()); } Collections.sort(list, new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { float num=(o2.getShuxue()+o2.getYingyu()+o2.getYuwen())-(o1.getShuxue()+o1.getYingyu()+o1.getYuwen()); int i=(int) num; return i; } }); initiate_IO(list); } private static void initiate_IO(List<Student> list) { BufferedWriter bw; StringBuffer sb=new StringBuffer(); for(Student stu:list) { sb.append(stu.toString()); sb.append("\r\n"); } try { bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("src\\stu.txt"),"utf-8"));//需要標明路徑 bw.write(sb.toString()); bw.flush(); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } private static List<Student> initiateList() { List<Student> list = new ArrayList<Student>(); Scanner scan = new Scanner(System.in); for (int i = 1; i <=5; i++) { System.out.println("請輸入第"+i+"學生信息：格式為 name 60 60 60"); String name = scan.next(); Float yuwen = scan.nextFloat(); Float shuxue = scan.nextFloat(); Float yingyu = scan.nextFloat(); Student stu = new Student(name, yuwen, shuxue, yingyu); list.add(stu); } return list; } } class Student { private String name; private float yuwen; private float shuxue; private float yingyu; public String getName() { return name; } public void setName(String name) { this.name = name; } public float getYuwen() { return yuwen; } public void setYuwen(float yuwen) { this.yuwen = yuwen; } public float getShuxue() { return shuxue; } public void setShuxue(float shuxue) { this.shuxue = shuxue; } public float getYingyu() { return yingyu; } public void setYingyu(float yingyu) { this.yingyu = yingyu; } public Student(String name, float yuwen, float shuxue, float yingyu) { super(); this.name = name; this.yuwen = yuwen; this.shuxue = shuxue; this.yingyu = yingyu; } public Student() { super(); } @Override public String toString() { return "Student [name=" + name + ", yuwen=" + yuwen + ", shuxue=" + shuxue + ", yingyu=" + yingyu + "]"; } }
Java中List集合排序的方法 比較器的使用 根據學生對象數序 語文 英語成績總和進行sort排序