Question

本人一初学Java ,，我想通过在控制台输入数字 来打印星号。调试后显示一错误：找不到符号，求解：

import java.io.*;
public class demo21{
public static void main(String args[]){
try{
InputStreamReader isr=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(isr);
System.out.println("输入第一个数");

String a1=br.readLine();
}
catch(Exception e)
{
e.printStackTrace();
}
class Per{

public void demo(int a){
for(int i=1;i<=4;i++){

for(int k=1;k<=4-i;k++){
System.out.print(" ");
}
for(int j=1;j<=(i-1)*2+1;j++){
System.out.print("*");
}

System.out.println();
}
}
}
Per o1=new Per();
o1.demo(a1);

}}

Answer 1

import java.io.*;
public class demo21 {
public static void main(String args[]) {
demo21 test = new demo21();
try {
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
System.out.println("输入第一个数");
String a1 = br.readLine();
int input = Integer.parseInt(a1);
test.demo(input);
} catch (Exception e) {
e.printStackTrace();
}
}
public void demo(int a) {
for (int i = 1; i <= 4; i++) {
for (int k = 1; k <= 4 - i; k++) {
System.out.print(" ");
}
for (int j = 1; j <= (i - 1) * 2 + 1; j++) {
System.out.print("*");
}
System.out.println();
}
}
}