Java打印实心、空心的三角形和菱形

1.实心三角形

代码：

 import java.util.Scanner;

 public class Test {

     public static void main(String[] args) {
         int rows;
         Scanner sc = new Scanner(System.in);
         System.out.println("Please input rows:");
         rows = sc.nextInt();
         sc.close();
         for (int i = 1; i <= rows; i++) {//控制打印行数
             for (int j = 1; j <= rows - i; j++) {//控制每行打印空格数
                 System.out.print(" ");
             }
             for (int j = 1; j <= i * 2 - 1; j++) {//控制打印星号数
                 System.out.print("*");
             }
             System.out.println();//每打一行，换行
         }
     }

 }

2.空心三角形

代码：

 import java.util.Scanner;

 public class Test {
     public static void main(String[] args) {
         int rows;
         Scanner sc = new Scanner(System.in);
         System.out.println("Please input rows:");
         rows = sc.nextInt();
         sc.close();
         for (int i = 1; i <= rows; i++) {
             for (int j = 1; j <= rows - i; j++) {
                 System.out.print(" ");
             }
             for (int j = 1; j <= 2 * i - 1; j++) {
                 if (i == 1 || i == rows) { // 如果是第一行或最后一行，打印所有星号
                     System.out.print("*");
                 } else if (j == 1 || j == 2 * i - 1) { // 如果是每行的第一个或者最后一个，打印星号
                     System.out.print("*");
                 } else { // 其余打印空格
                     System.out.print(" ");
                 }
             }
             System.out.println();
         }
     }
 }

3.实心菱形

代码：

 import java.util.Scanner;

 public class Test {
     public static void main(String[] args) {
         int rows;
         Scanner sc = new Scanner(System.in);
         System.out.println("Please input odd rows:");// 只能是奇数行
         rows = (sc.nextInt() + 1) / 2;// 上半部分行数
         sc.close();
         for (int i = 1; i <= rows; i++) {
             for (int j = 1; j <= rows - i; j++) {
                 System.out.print(" ");
             }
             for (int j = 1; j <= 2 * i - 1; j++) {
                 System.out.print("*");
             }
             System.out.println();
         }
         for (int i = rows - 1; i >= 1; i--) { // 下半部分不可重复打印上半部分最后一行，i=rows-1)
             for (int j = 1; j <= rows - i; j++) {
                 System.out.print(" ");
             }
             for (int j = 1; j <= 2 * i - 1; j++) {
                 System.out.print("*");
             }
             System.out.println();
         }
     }
 }

4.空心菱形

代码：

 import java.util.Scanner;

 public class Test {
     public static void main(String[] args) {
         int rows;
         Scanner sc = new Scanner(System.in);
         System.out.println("Please input odd rows:");// 只能是奇数行
         rows = (sc.nextInt() + 1) / 2;// 上半部分行数
         sc.close();
         sc.close();
         for (int i = 1; i <= rows; i++) {
             for (int j = 1; j <= rows - i; j++) {
                 System.out.print(" ");
             }
             for (int j = 1; j <= 2 * i - 1; j++) {
                 if (i == 1) {
                     System.out.print("*");
                 } else if (j == 1 || j == 2 * i - 1) {
                     System.out.print("*");
                 } else {
                     System.out.print(" ");
                 }
             }
             System.out.println();
         }
         for (int i = rows - 1; i >= 1; i--) {// 此处只需i=rows-1即可
             for (int j = 1; j <= rows - i; j++) {
                 System.out.print(" ");
             }
             for (int j = 1; j <= 2 * i - 1; j++) {
                 if (i == 1) {
                     System.out.print("*");
                 } else if (j == 1 || j == 2 * i - 1) {
                     System.out.print("*");
                 } else {
                     System.out.print(" ");
                 }
             }
             System.out.println();
         }
     }
 }