String s = "";
for (int i = 0; i < b; i++)
{
s += a.toString();
}
System.out.println(s);

Scanner input = new Scanner(System.in);
int a = input.nextInt();
int b = input.nextInt();String s = "";
for (int i = 0; i < b; i++)
{
s += a.toString();
}
System.out.println(s);

把这些放在main里面就可以了。

    public static void dowork(int a,int b)
    {
        for(int i=0;i<b;i++)
        {
            System.out.print(a);
        }
    }

注意，输出的不是一个数

首先，重复从控制台接受两个int类型的数据，而且限制a的大小为0-9；其次就是用字符串的累加b个a即可。
参考代码：

 import java.util.Scanner;

public class PrintNumber {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);  
        System.out.println("输入数字a(a<10):");  
        int a = input.nextInt();
        while(a>9||a<0){
            System.out.println("请重新输入数字a(a<10):");  
            a = input.nextInt();
        }
        System.out.println("输入任意数字b:");  
        int b = input.nextInt();
        String result = generateNumber(a,b);
        System.out.println("生成的数据为:"+result);
        input.close();
    }

    public static String generateNumber(int a, int b) {
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < b; i++) {
            buffer.append(a);
        }
        return buffer.toString();
    }
}

 public class text {

    public static void main(String[] args) {
        System.out.println("请输入a");
        Scanner a1 = new Scanner(System.in);
        String a = a1.next();
        System.out.println("请输入b");
        Scanner b1 = new Scanner(System.in);
        String b = b1.next();
        int j = Integer.parseInt(b);
        for(int i = 0;i<j;i++){
            System.out.print("a");
        }
    }

}

import java.io.*;
public class test
{
public static void main(String args[])
{
try
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter your a");
String str1=br.readLine();
System.out.println("Enter your b");
String str2=br.readLine();
result(str1,str2);
}
catch(Exception e)
{System.out.println("io is error");}
}

public static void result(String str1,String str2)
{
int a=Integer.parseInt(str1);
int b=Integer.parseInt(str2);

int c=0;
int k=1;
for(int i=0;i<b;i++)
{
k=k*10;
System.out.println("K:"+k);
c=c+k*a;
}

System.out.println("so you result c is :"+c);

}

转成字符串叠加输出比较好