Question

我已经制作了一个简单的Java应用程序来打印文本文件然后应该终止。我试图使用return statemend但根本没用。所以我使用了system.exit（0），但不是退出应用程序，它进入无限循环...... 这是我的代码：有人可以告诉我出了什么问题吗？

package com.example.testprinterdemo;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;

import com.pda3505.Service.CaptureService;
import com.pda3505.printer.PrinterClassSerialPort;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;


public class MainActivity extends Activity {

    public static PrinterClassSerialPort printerClass = null;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        init();

        printerClass.write(new byte[] { 0x1d, 0x21,0x00,0x00});
        printerClass.write(new byte[] { 0x1b, 0x26, 0x00 });


        BufferedReader reader = null;
        try {reader = new BufferedReader(new FileReader("/mnt/sdcard/temp.txt"));} 
        catch (FileNotFoundException e) {e.printStackTrace();}
        String line = null;
        try {line = reader.readLine();} 
        catch (IOException e) {e.printStackTrace();}
        while(line!=null) {
            printerClass.printText(line);
            printerClass.printText("\n");
            try {line = reader.readLine();} 
            catch (IOException e) {e.printStackTrace();}
        }
        system.exit(0);
    }


    private void init() {       

        printerClass = new PrinterClassSerialPort(new Handler());
        printerClass.open(this);

        Intent newIntent = new Intent(MainActivity.this, CaptureService.class);
        newIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startService(newIntent);

    }

}

Answer 1

>>> import os
>>> path = "path to a word document"
>>> os.path.isfile(path)
True
>>> os.path.splitext(path)[1] == ".docx" # test if the extension is .docx
True

在您的方法中，行永远不会为空，它可以是try{ //never hard code the file path in Android. String filePath = Environment.getExternalStorageDirectory().getAbsolutePath()+File.separator+"temp.txt"; BufferedReader reader = new BufferedReader(new FileReader(filePath)); while (true){ String line = reader.readLine(); if(line.length() > 0){ printerClass.printText(line); printerClass.printText("\n"); }else{ break; //you can use return too } } }catch (IOException e){ e.printStackTrace(); }，也可以是""或" "等，但永远不会为空。所以听长度并打破循环

如果您可以将代码置于单个try块下，请避免使用多个try catch块。请正确调整变量范围，不要在不使用变量的范围之外声明变量，因为它会导致JAVA垃圾收集器出现问题/

java exit app导致无限循环

1 个答案: