Java 将对象按某属性排列

使用集合类arrayList 与comparator实现。
Comparator称之为匿名内部类，只需使用一次，不需要多次创建对象。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
class Student {
     String name;
     String gender;
     int age;
     float gpa;
     String grade; //应设为私有变量，为方便省略之

    public Student(String name, String gender, int age, float gpa,String grade){
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.gpa = gpa;
        this.grade = grade;
    }
    public void show() {
        System.out.println("Name: "+this.name+", gender: "+this.gender+", age: "+this.age+", GPA: "+this.gpa+", Grade: "+this.grade);
    }
}
public class Console {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Comparator<Student> comparator = new Comparator<Student>() {

            @Override
            public int compare(Student o1, Student o2) {
                // TODO Auto-generated method stub

                /*
                 * 设置compare函数应严密，考虑相等情况下下一考虑属性
                 * 数值（int，float， double）可考虑直接相减
                 * 字符串可采用compareTo函数
                 */
                int answer;
                if (o1.gpa!=o2.gpa) {
                    answer = (int) (o1.gpa*10-o2.gpa*10);
                }
                else {
                    answer = o1.grade.compareTo(o2.grade);
                }
                System.out.println(answer);
                return answer;
            }
        };
        ArrayList<Student> students = new ArrayList<Student>();
        //float属性赋值需加f

        Student student1 = new Student("a", "m", 18, 3.8f, "2008");
        Student student2 = new Student("b", "f", 19, 4.5f, "2007");
        Student student3 = new Student("c", "m", 20, 4.4f, "2006");
        Student student4 = new Student("d", "f", 14, 4.2f, "2012");
        Student student5 = new Student("e", "f", 15, 4.0f, "2011");
        Student student6 = new Student("f", "f", 16, 4.0f, "2010");
        Student student7 = new Student("g", "m", 17, 4.2f, "2009");
        Student student8 = new Student("h", "m", 15, 3.9f, "2011");
        Student student9 = new Student("i", "f", 18, 3.9f, "2008");
        Student student10 = new Student("j", "m", 20, 3.7f, "2006");
        students.add(student1);
        students.add(student2);
        students.add(student3);
        students.add(student4);
        students.add(student5);
        students.add(student6);
        students.add(student7);
        students.add(student8);
        students.add(student9);
        students.add(student10);
        Collections.sort(students,comparator);
        for (Student student : students) {
            student.show();
        }


    }

}

another solution:
    

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.SortedSet;
import java.util.TreeSet;
class Student implements Comparable<Student>{
     String name;
     String gender;
     int age;
     float gpa;
     String grade; //应设为私有变量，为方便省略之
    public Student(String name, String gender, int age, float gpa,String grade){
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.gpa = gpa;
        this.grade = grade;
    }
    public void show() {
        System.out.println("Name: "+this.name+", gender: "+this.gender+", age: "+this.age+", GPA: "+this.gpa+", Grade: "+this.grade);
    }
    @Override
    public int compareTo(Student o) {
        // TODO Auto-generated method stub
        int answer;
        if (this.gpa!=o.gpa) {
            answer = (int) (this.gpa*10-o.gpa*10);
        }
        else {
            answer = this.grade.compareTo(o.grade);
        }
        System.out.println(answer);
        return answer;
    }
}
public class Console {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        TreeSet<Student> students = new TreeSet<Student>();
        //float属性赋值需加f
        Student student1 = new Student("a", "m", 18, 3.8f, "2008");
        Student student2 = new Student("b", "f", 19, 4.5f, "2007");
        Student student3 = new Student("c", "m", 20, 4.4f, "2006");
        Student student4 = new Student("d", "f", 14, 4.2f, "2012");
        Student student5 = new Student("e", "f", 15, 4.0f, "2011");
        Student student6 = new Student("f", "f", 16, 4.0f, "2010");
        Student student7 = new Student("g", "m", 17, 4.2f, "2009");
        Student student8 = new Student("h", "m", 15, 3.9f, "2011");
        Student student9 = new Student("i", "f", 18, 3.9f, "2008");
        Student student10 = new Student("j", "m", 20, 3.7f, "2006");
        students.add(student1);
        students.add(student2);
        students.add(student3);
        students.add(student4);
        students.add(student5);
        students.add(student6);
        students.add(student7);
        students.add(student8);
        students.add(student9);
        students.add(student10);
        for (Student student : students) {
            student.show();
        }


    }

}