1 Số bài tập cơ bản trong java với mảng

import java.io.*;
import java.util.Scanner;
public class CanBan 
{
    static int n;
    static int a[],b[];
    static int i;
    private static Scanner scanin;
    public static void nhapmang()
    {
        Scanner scanin = new Scanner(System.in); 
        System.out.println("nhap so phan tu cua mang");
        n = scanin.nextInt(); 
        a = new int[n];
        for ( i = 0 ; i < n ; i ++)
        {
            System.out.println("a[" + i+ "]=");
            a[i]=scanin.nextInt(); 
        }
    }
    public static void xuatmang()
    {
        for ( i = 0 ; i < n ; i ++)
        {
            System.out.println("a["+i+"]="+a[i]+"\n");
        }
    }
    public static int tinhtong()
    {
        int tong = 0;
        for ( i = 0 ; i < n ; i ++)
        {
            tong = a[i] + tong;
        }
        return tong;
    }
    public static void chen()
    {
        int k,tmp;
        b = new int[n+1];
        scanin = new Scanner(System.in);
        System.out.println("nhap vao vi tri muon chen");
        k = scanin.nextInt();
        System.out.println("\nnhap so muon chen");
        tmp = scanin.nextInt();
        for ( i = 0 ; i < k ; i++)
        {
            b[i]=a[i];
        }
        b[i++]= tmp;
        for ( i = k+1 ; i <= n ; i++)
        {
            b[i]=a[i-1];
        }
        for ( i = 0 ; i < n+1 ; i ++)
        {
            System.out.println("b["+i+"]="+b[i]+"\n");
        }
    }
    public static void xoa()
    {
        int k;
        b = new int[n-1];
        scanin = new Scanner(System.in);
        System.out.println("nhap vao vi tri muon xoa");
        k = scanin.nextInt();
        for ( i = 0 ; i < k ; i ++)
            b[i]=a[i];
        for ( i = k + 1 ; i < n ; i++ )
            b[i-1]=a[i];
        for ( i = 0 ; i < n-1 ; i ++)
            System.out.println("b["+i+"]="+b[i]+"\n");
    }    
    public static void timso()
    {
     Scanner scanin = new Scanner(System.in); 		System.out.println("\n nhap so muon tim");
		tmp = scanin.nextInt();
		dem=0;
		for ( i = 0 ; i < n ; i ++)
			if ( a[i] == tmp)
			{
				dem++;
				System.out.println("\nSo can tim o vi tri "+i);
			}
		if ( dem == 0 )
			System.out.println("Khong co so can tim ");
    }
    public static void sapxep()
    {
        int tmp;
        int j;
        for ( int i = 0 ; i < n-1 ; i ++)
            for ( j = i ; j < n ; j ++)
                if (a[i] < a[j])
                {
                    tmp = a[i];
                    a[i]=a[j];
                    a[j]=tmp;
                }
    }    
    public static void main(String[] args)
    {
        nhapmang();
    //    xuatmang();
    //    System.out.println("\n tong la "+tinhtong());
    //    chen();
    //    xuatmang();
    //    xoa();
    //    timso();
    //    sapxep();
    //    xuatmang();
    }


}