SelectionSort

public class SelectionSort {
	public static void sort(Comparable[] a){
		int N=a.length;
		for(int i=0;i<N;++i){
			for(int j=i+1;j<N;++j){
				if(less(a[i],a[j])){
					exch(a,i,j);
				}
			}
		}
	}
	public static boolean less(Comparable v,Comparable w){
		if(v.compareTo(w)<0) return true;
		else return false;
		}
	public static void exch(Comparable[] a,int i,int j){
			Comparable temp=a[i];
			a[i]=a[j];
			a[j]=temp;
	}
	public static boolean isSort(Comparable[] a){
		for(int i=1;i<a.length;++i){
			if(less(a[i-1],a[i]))return false;
		}
		return true;
	}
}

Students implements Comparable

public class Student implements Comparable<Student> {
	private int score;
	private String name;
	public Student(){
		score=0;
		name="unknow";
	}
	public Student(int score,String name){
		this.score=score;
	    this.name=name;
	}
	public String toString(){
		return "Score: "+score+" Name: "+name;
	}
	@Override
	public int compareTo(Student that){
		if(this.score<that.score) return -1;
		else if(this.score>that.score) return 1;
		else return 0;
	}
}

TestCase

public class TestSelectionSort {
	public static void main(String[] args){
	Comparable[] a=new Student[20];
	a[0]=new Student(72,"Almin");
	a[1]=new Student(78,"Peter");
	a[2]=new Student(89,"Bob");
	a[3]=new Student(91,"Eric");
	a[4]=new Student(56,"Adam");
	a[5]=new Student(69,"Alpha");
	a[6]=new Student(98,"Allen");
	a[7]=new Student(90,"Emily");
	a[8]=new Student(79,"Emma");
	a[9]=new Student(83,"Yui");
	a[10]=new Student(100,"Mikasa");
	a[11]=new Student(77,"Max");
	a[12]=new Student(85,"Noah");
	a[13]=new Student(65,"Kun");
	a[14]=new Student(74,"Beta");
	a[15]=new Student(76,"Rebeca");
	a[16]=new Student(89,"Lifa");
	a[17]=new Student(81,"Ben");
	a[18]=new Student(70,"Petera");
	a[19]=new Student(80,"Run");
	SelectionSort.sort(a);
	Boolean x=SelectionSort.isSort(a);
	System.out.println(x);
	int N=a.length;
	for(int i=0;i<N;++i){
		System.out.println(a[i].toString());
	}
	}
}