java基础_案例循环打印输出

案例1：打印一行星号

public class Demo {
    public static void main(String[] args) {
        System.out.println("输入数字");
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        for (int i=0;i<a;i++){
            System.out.print("*");
        }
    }
}

结果：

案例二：打印矩形

public class Demo {
    public static void main(String[] args) {
        System.out.println("请输入行数");
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        System.out.println("请输入列数");
        int b = sc.nextInt();
        for (int i = 0;i<a;i++){//控制行
            for (int j = 0;j<b;j++){//控制列
                System.out.print("* ");
            }
            System.out.println("");
        }
    }
}

结果：

案例三：打印直角三角形

public class Demo {
    public static void main(String[] args) {
        System.out.println("请输入三角形的行数：");
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        for (int i =1 ;i<=a;i++){
            for (int j = 1;j<=i;j++){
                System.out.print("* ");
            }
            System.out.println("");
        }
    }
}

结果：

案例四：打印等腰三角形

首先得找到规律：

public class Demo {
    public static void main(String[] args) {
        System.out.println("请输入行数");
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();

        for (int i =1;i<=a;i++){
            for (int j =1;j<=a-i;j++){
                System.out.print(" ");//打印空格
            }
            for (int j =1;j<=2*i-1;j++){
                System.out.print("*");//打印星号
            }
            System.out.println();
        }
    }
}

结果：

案例五：打印菱形

找到规律：

1 2

public class Demo {
    public static void main(String[] args) {
        System.out.println("请输入行数");
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();

        for (int i =1;i<=a;i++){
            for (int j =1;j<=a-i;j++){
                System.out.print(" ");//打印上半部分空格
            }
            for (int j =1;j<=2*i-1;j++){
                System.out.print("*");//打印上半部分星号
            }
            System.out.println();
        }
        for (int i = a-1;i>=1;i--){
            for (int k = 1;k<=(a-i);k++){
                System.out.print(" ");//打印下半部分空格
            }
            for (int j = 1;j<=2*i-1;j++){
                System.out.print("*");//下半部分星号
            }
            System.out.println();
        }
        System.out.println();
    }
}

结果：