sort排序
在java中，可以使用sort方法快捷的進行排序。
數組的sort排序
- sort方法時Arrays類中的靜態方法。可以直接利用類名進行調用。
Arrays類中sort的常用方法：
static void sort(type [] a, int fromIndex, int toIndex)
對指定數組的指定範圍按數字升序進行排序。
type 可以指定爲int,float,double,long,byte等。
a - 要排序的數組
fromIndex - 要排序的第一個元素的索引（包括）
toIndex - 要排序的最後一個元素的索引（不包括）
static void sort(type [] a)
對指定的 type型數組按數字升序進行排序。
默認爲升序排列
for example
import java.util.Arrays;
import java.util.Scanner;
public class test {
public static void main(String[] args) {
Scanner scanner= new Scanner(System.in);
int n = scanner.nextInt();
long num[] =new long [n];
for(int i=0;i<n;i++){
num[i] = scanner.nextLong();
}
Arrays.sort(num,0,n);
for(int i=0;i<n;i++)
System.out.print(num[i]+" ");
}
}
輸入：
5
1 3 6 2 4
輸出：
1 2 3 4 6
利用sort函數對自定義對象的數組進行排序
對自定義的對象的數組進行sort排序，一般需要用到Comparable或是Comparator接口。首先在這裏總結一下這兩個接口的區別：
- Comparable可以認爲是一個內比較器，實現了Comparable接口的類有一個特點，就是這些類是可以和自己比較的，至於具體和另一個實現了Comparable接口的類如何比較，則依賴compareTo方法的實現，compareTo方法也被稱爲自然比較方法。
compareTo方法的返回值是int，有三種情況：
1、比較者大於被比較者（也就是compareTo方法裏面的對象），那麼返回正整數
2、比較者等於被比較者，那麼返回0
3、比較者小於被比較者，那麼返回負整數
for example：
對一些學生根據總分成績排序輸出，總成績相同時，根據語文成績高低排序，如果語文成績也相同時，依次按照數學，英語成績進行排序。
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
import javax.swing.plaf.synth.SynthStyle;
//外比較器
class cmp implements Comparator<Student>{
// 比較規則
@Override
public int compare(Student o1, Student o2) {
if(o1.getTotalScore()!=o2.getTotalScore())
return o1.getTotalScore()>o2.getTotalScore()?-1:1;
else if(o1.getChineseScore()!=o2.getChineseScore())
return o1.getChineseScore()>o2.getChineseScore()?-1:1;
else if(o1.getMathScore()!=o2.getMathScore())
return o1.getMathScore()>o2.getMathScore()?-1:1;
else
return o1.getEnglishScore()>o2.getEnglishScore()?-1:1;
}
}
class Student {
private String name ;
private double totalScore;
private double chineseScore;
private double mathScore;
private double englishScore;
//get 和set方法
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getTotalScore() {
return totalScore;
}
public void setTotalScore(double totalScore) {
this.totalScore = totalScore;
}
public double getChineseScore() {
return chineseScore;
}
public void setChineseScore(double chineseScore) {
this.chineseScore = chineseScore;
}
public double getMathScore() {
return mathScore;
}
public void setMathScore(double mathScore) {
this.mathScore = mathScore;
}
public double getEnglishScore() {
return englishScore;
}
public void setEnglishScore(double englishScore) {
this.englishScore = englishScore;
}
public Student(){}
public Student(String name ,double chineseScore,double mathScore,double englishScore){
this.name =name;
this.totalScore=chineseScore+mathScore+englishScore;
this.chineseScore =chineseScore;
this.mathScore=mathScore;
this.englishScore=englishScore;
}
@Override
public String toString() {
return name + " 總分："+totalScore+" 語文: "+chineseScore+" 數學: "+mathScore+" 英語 :"+englishScore;
}
}
public class test {
public static void main(String[] args) {
Scanner sc =new Scanner(System.in);
int n= sc.nextInt();
Student stu[] = new Student[n];
for(int i=0;i<n;i++){
String name;
name =sc.next();
double chineseScore, mathScore, englishScore;
chineseScore =sc.nextDouble();
mathScore =sc.nextDouble();
englishScore =sc.nextDouble();
stu[i] = new Student(name, chineseScore, mathScore, englishScore);
}
Arrays.sort(stu,new cmp());
for(int i=0;i<n;i++){
System.out.println(stu[i].toString());
}
}
}
輸入：
3
小王 120 110 135
小李 115 135 116
小張 122 126 131
輸出：
小張 總分：379.0 語文: 122.0 數學: 126.0 英語 :131.0
小李 總分：366.0 語文: 115.0 數學: 135.0 英語 :116.0
小王 總分：365.0 語文: 120.0 數學: 110.0 英語 :135.0
當然爲了寫起來方便，外比較器可以這樣寫：
Arrays.sort(stu,new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
if(o1.getTotalScore()!=o2.getTotalScore())
return o1.getTotalScore()>o2.getTotalScore()?-1:1;
else if(o1.getChineseScore()!=o2.getChineseScore())
return o1.getChineseScore()>o2.getChineseScore()?-1:1;
else if(o1.getMathScore()!=o2.getMathScore())
return o1.getMathScore()>o2.getMathScore()?-1:1;
else
return o1.getEnglishScore()>o2.getEnglishScore()?-1:1;
}
});
集合的sort排序
- 對於常用的vector,list等也可以利用sort進行排序：
（1）list中的對象已經實現了Comparable接口，說明list中的那種對象是可比較的類型，支持自己和自己比較的，那麼可以直接調用 Collections.sort(list)；進行排序。例如常見的Integer,Float,Double類型等。
（2）如果list中的類沒有實現Comparable接口，則需要藉助外比較器，實現Comparator接口的類的對象
for example
例子和上面實現的相同，只是用的是vector存放student對象，然後排序。
import java.awt.List;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Vector;
class cmp implements Comparator<Student>{
@Override
public int compare(Student o1, Student o2) {
if(o1.getTotalScore()!=o2.getTotalScore())
return o1.getTotalScore()>o2.getTotalScore()?-1:1;
else if(o1.getChineseScore()!=o2.getChineseScore())
return o1.getChineseScore()>o2.getChineseScore()?-1:1;
else if(o1.getMathScore()!=o2.getMathScore())
return o1.getMathScore()>o2.getMathScore()?-1:1;
else
return o1.getEnglishScore()>o2.getEnglishScore()?-1:1;
}
}
class Student {
private String name ;
private double totalScore;
private double chineseScore;
private double mathScore;
private double englishScore;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getTotalScore() {
return totalScore;
}
public void setTotalScore(double totalScore) {
this.totalScore = totalScore;
}
public double getChineseScore() {
return chineseScore;
}
public void setChineseScore(double chineseScore) {
this.chineseScore = chineseScore;
}
public double getMathScore() {
return mathScore;
}
public void setMathScore(double mathScore) {
this.mathScore = mathScore;
}
public double getEnglishScore() {
return englishScore;
}
public void setEnglishScore(double englishScore) {
this.englishScore = englishScore;
}
public Student(){}
public Student(String name ,double chineseScore,double mathScore,double englishScore){
this.name =name;
this.totalScore=chineseScore+mathScore+englishScore;
this.chineseScore =chineseScore;
this.mathScore=mathScore;
this.englishScore=englishScore;
}
@Override
public String toString() {
return name + " 總分："+totalScore+" 語文: "+chineseScore+" 數學: "+mathScore+" 英語 :"+englishScore;
}
}
public class test {
public static void main(String[] args) {
Scanner sc =new Scanner(System.in);
int n= sc.nextInt();
Vector<Student> vc =new Vector<Student>();
for(int i=0;i<n;i++){
String name;
name =sc.next();
double chineseScore, mathScore, englishScore;
chineseScore =sc.nextDouble();
mathScore =sc.nextDouble();
englishScore =sc.nextDouble();
vc.addElement( new Student(name, chineseScore, mathScore, englishScore));
}
Collections.sort(vc,new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
if(o1.getTotalScore()!=o2.getTotalScore())
return o1.getTotalScore()>o2.getTotalScore()?-1:1;
else if(o1.getChineseScore()!=o2.getChineseScore())
return o1.getChineseScore()>o2.getChineseScore()?-1:1;
else if(o1.getMathScore()!=o2.getMathScore())
return o1.getMathScore()>o2.getMathScore()?-1:1;
else
return o1.getEnglishScore()>o2.getEnglishScore()?-1:1;
}
});
Iterator<Student> iterator = vc.iterator();
while(iterator.hasNext()){
System.out.println(iterator.next().toString());
}
}
}