JAVA基础学习（5）之数组

5数组

• 5.1数组
  • 5.1.1初识数组
    • 　　

       //        输出大于平均数的所有数
               Scanner in = new Scanner(System.in);
               int n;
               int[] a = new int[100];
               int count = 0;
               double sum = 0;
               while ((n = in.nextInt()) != -1)
               {
                   a[count] = n;
                   sum += n;
                   count++;
               }
               if (count > 0)
               {
      
                   for (int i = 0; i < count; i++)
                   {
                       if (a[i] > (sum / count))
                       {
                           System.out.println(a[i]);
                       }
                   }
                   System.out.println("平均数为：" + sum / count);
               }

  • 5.1.2创建数组
  • 5.1.3数组的元素
    • 数组的大小不能改变
  • 5.1.4数组变量
    • 普通变量所有者
    • 数组变量管理者

    •  int[] a = new int[10];
               a[0] = 5;
               int[] b = a;
               System.out.println(a[0]);
               System.out.println(b[0]);
               for (int i = 0; i < b.length; i++)
               {
                   if (i == b.length - 1)
                   {
                       System.out.println(b[i]);
                       break;
                   }
                   System.out.print(b[i]);
               }
               System.out.println(a);
               System.out.println(b);

• 5.2数组计算
  • 5.2.1投票统计
    • 　　

       // 投票统计
               Scanner in = new Scanner(System.in);
               int x;
               int[] numbers = new int[10];
               while ((x = in.nextInt()) != -1)
               {
                   if ((x >= 0) && (x <= 9))
                   {
                       numbers[x]++;
                   }
               }
               for (int i = 0; i < numbers.length; i++)
               {
                   System.out.println(i + ": " + numbers[i]);
               }

  • 5.2.2遍历数组
    • 　　

       // 遍历数组
               Scanner in = new Scanner(System.in);
               int x = in.nextInt();
               int[] a =
               { 3, 4, 5, 6, 7, 8, 32, 45 };
               int loc = -1;
               boolean flag = false;
               for (int i = 0; i < a.length; i++)
               {
                   if (x == a[i])
                   {
                       loc = i;
                       break;
                   }
               }
               for (int k : a)
               {
                   if (k == x)
                   {
                       flag = true;
                   }
               }
               if (flag)
               {
                   System.out.println(x + "存在");
                   System.out.println(x + "在第" + (loc + 1) + "个");
               } else
               {
                   System.out.println(x + "不在其中");
               }

  • 5.2.3素数
    • 　　

       // 素数
               Scanner in = new Scanner(System.in);
               System.out.println("请输入一个数：");
               int x = in.nextInt();
               boolean isPrime = true;
               if (x == 1 || x % 2 == 0 && x != 2)
               {
                   isPrime = false;
               } else
               {
                   for (int i = 3; i < Math.sqrt(x); i+=2)
                   {
                       if (x%i==0)
                       {
                           isPrime=false;
                           break;
                       }
                   }
               }
               if (isPrime)
               {
                   System.out.println(x+"是素数");
               }else
               {
                   System.out.println(x+"不是素数");
               }

• 5.3二维数组
  • OX棋