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最近在学IO流的标准输入输出流，做了一个“实现Scanner类的效果”的练习。可是报错

 

MyInput.java中（该类用来模拟Scanner）

package com.pacoco.learnIO;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class MyInput {
    public String nextString() {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        try {
            return br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public int nextInt(){
        return Integer.parseInt(nextString());
    }

    public float nextFloat(){
        return Float.parseFloat(nextString());
    }
}

 

在MyInputTest.java中

package com.pacoco.learnIO;

public class MyInputTest {
    public static void main(String[] args) {
        MyInput mi = new MyInput();
        System.out.println(mi.nextFloat());
        System.out.println(mi.nextString());
    }
}

 

输入输出：

 

求助！