编写java程序，输入学生的人数，然后逐个输入每个学生的姓名和成绩。统计成绩的降序输出学生的姓名。

import java.util.Scanner;
public class Student{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
System.out.println("请输入学生的人数....");
int num = sc.nextInt();
int[] arr = new int[num];
double[] chengji_arr = new double[num]; //存放成绩的
String[] String_arr = new String[num]; //存放姓名的
String chengjis = "";
String names = "";
for(int i = 0; i < arr.length && i < String_arr.length && i < chengji_arr.length; i++){
arr[i] = i;
int s = 0;
Students st = new Students();
System.out.println("请输入第"+(arr[i]+1)+"个学生的序号！");
st.setId(sc.nextInt());
System.out.println("请输入第"+(arr[i]+1)+"个学生的姓名！");
st.setName(sc.next());
System.out.println("请输入第"+(arr[i]+1)+"个学生的成绩！");
st.setChengji(sc.nextDouble());
String_arr[i] = st.getName(); //保存成绩
chengji_arr[i] = st.getChengji();
}
int max = 0;
int tmp = 0;
for (int i = 0; i < chengji_arr.length; i++) {
max = i;
for (int j = i + 1; j < chengji_arr.length; j++) {
if (chengji_arr[max] < chengji_arr[j])
max = j;// 记下较大数位置，再次比较，直到最大
}
if (i != max) {
tmp = (int)chengji_arr[i];
chengji_arr[i] = chengji_arr[max];
chengji_arr[max] = tmp;
}

}
for (int i = 0; i < chengji_arr.length; i++)
System.out.print("成绩为："+chengji_arr[i] + " ");
}
}
class Students{
private int id;
private String name;
private double chengji;
public void setId(int id){
this.id = id;
}
public int getId(){
return id;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return name;
}
public void setChengji(double chengji){
this.chengji = chengji;
}
public double getChengji(){
return chengji;
}
}
//代码没有交换学生数组下标，麻烦提问者再修改一下吧，真的要睡了，明天继续上班，抱歉，只能帮你到这里了。