Java 程序小作业 输入 字符串转化

import java.util.Scanner;
import java.io.*;
public class Test {

public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("输入你的当前账户");
Scanner readern = new Scanner(System.in);
int n = readern.nextInt();
System.out.println("当前账户余额：100000.00元");
System.out.println("请选择功能：");
System.out.println("1.存钱     2. 取钱    0. 退出");
Scanner readernum = new Scanner(System.in);
int num = readernum.nextInt();
if(num>2)
System.out.println("选择错误！");
else if(num==0)
System.out.println("再见！");
else if(num==1) {
System.out.println("请输入存款金额：");
Scanner reader = new Scanner(System.in);
String str= reader.nextLine();
boolean isNum = str.matches("[0-9]+");
if(!isNum)
System.out.println("输入有误！");
else {
int sum = Integer.valueOf(str).intValue()+100000;
System.out.println("当前账户余额："+sum);
}

}
else if(num==2) {
System.out.println("请输入取款金额：");
Scanner reader = new Scanner(System.in);
String str= reader.nextLine();
int sum = Integer.valueOf(str).intValue();
if(sum>100000)
System.out.println("余额不足！");
else {
sum=100000-sum;
System.out.println("当前账户余额："+sum);
}
}

}

}