Question

java 用FOR循环画菱形

*
***
*****
*******
******
****
***
*

这样的，

Answer 1

System.out.print("请输入要打印的菱形行数：");
Scanner input = new Scanner(System.in);
int itline = 0;
while (true) {
itline = input.nextInt();
if (itline <= 2) {
System.out.println("输入的行数无效，请重新输入大于等于3的行数");
} else if(itline%2 == 0) {
System.out.println("输入的行数无效，请重新输入奇数");
} else {
// 每一轮循环，代表一行
for (int line = 1; line <= itline; line++) {
int num;
// 打印首位数字前的空格
for (num = 1; num <= itline - line; num++) {
System.out.print(" ");
}
// 打印上三角形部分
for (num = 1, i = 1; num <= line * 2 - 1; num++) {
System.out.print("*");
}
System.out.println();
}
// 每一轮循环，代表一行
for (int line = itline-1; line >= 1; line--) {
int num;
// 打印首位数字前的空格
for (num = itline - line; num >= 1; num--) {
System.out.print(" ");
}
// 打印下三角形部分
for (num = line * 2 - 1, i = 1; num >= 1; num--) {//num = line * 2 - 1，而非line * 2
System.out.print("*");
}
System.out.println();
}
break;
}
}

Answer 2

具体实现代码如下：希望对你有帮助
class Demo
{
public static void main(String args[])throws Exception
{
for(int i=1;i<=5;i++)
{
for(int j=1;j<=5-i;j++)
System.out.print(" ");
for(int k=1;k<=2*i-1;k++)
System.out.print('*');
System.out.println();
}
for(int i=1;i<=4;i++)
{
for(int j=1;j<=i;j++)
System.out.print(" ");
for(int k=7;k>=2*i-1;k--)
System.out.print('*');
System.out.println();
}
}
}