Java 字符串替换()给出空指针异常
我哪里出错了??无论我做什么,它都会在String.replace()上显示空指针异常 我想替换文件中的字符,并将更改的内容写入其他文件。。虽然很简单,但我不会写。请帮忙Java 字符串替换()给出空指针异常,java,Java,我哪里出错了??无论我做什么,它都会在String.replace()上显示空指针异常 我想替换文件中的字符,并将更改的内容写入其他文件。。虽然很简单,但我不会写。请帮忙 package tinku; /* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and o
package tinku;
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.util.Scanner;
/**
*
* @author gajasurve
*/
public class Tinku {
static int i;
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws FileNotFoundException, IOException {
// TODO code application logic here
String str;
final String Y;
String Key;
FileOutputStream fos = new FileOutputStream("/home/gajasurve/Desktop/done2.txt");
DataOutputStream output = new DataOutputStream(fos);
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
System.out.println("\n Enter Complete File Path with Extension (ex: /home/gajasurve/Desktop/info.txt) : ");
String Source;
Source=r.readLine();
System.out.print("Enter Key Element to Find In the File ");
Key=r.readLine();
File f= new File(Source);
LineNumberReader lr= new LineNumberReader(new FileReader(f));
while((str=lr.readLine())!=null)
{
if(str.contains(Key))
{
i=lr.getLineNumber();
System.out.print("The Entered Key Element Can B Found In " + i + " Line");
}
}
System.out.println("Do u wish to change the Key Element? Y|N");
String Dec= r.readLine();
switch (Dec) {
case "Y" :
System.out.print("Enter New Key Element to Replace");
String d2;
d2 = r.readLine();
str= str.replaceAll(Key, d2); //NPE here
System.out.println(str);
break;
}
}
}
当您运行while循环时,退出条件是循环在
str
变为null
时结束,因此当您下次尝试访问str
时,它将变为null,并给出NullPointerException
您可以通过在replaceAll()
代码周围运行类似的while
循环来修复它,或者可以移动所有内容,直到replaceAll()
方法调用在while
循环中为止。(注意:这将询问您是否要为每次事件更换键
)
可能的固定代码:
package tinku;
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
import java.io.*;
/**
*
* @author gajasurve
*/
public class Tinku {
static int i;
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws FileNotFoundException, IOException {
// TODO code application logic here
String str;
final String Y;
String Key;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("\n Enter Complete File Path with Extension (ex: /home/gajasurve/Desktop/info.txt) : ");
String Source;
Source = br.readLine();
File f= new File(Source);
LineNumberReader lr= new LineNumberReader(new FileReader(f));
System.out.print("Enter Key Element to Find In the File : ");
Key = br.readLine();
while((str = lr.readLine()) != null) {
if(str.contains(Key)) {
i = lr.getLineNumber();
System.out.println("The Entered Key Element Can B Found In " + i + " Line");
}
}
lr.close();
System.out.println("Do u wish to change the Key Element? Y|N");
String Dec= br.readLine();
switch(Dec) {
case "Y" : {
System.out.print("Enter String to replace Key with : ");
String d2;
d2 = br.readLine();
lr= new LineNumberReader(new FileReader(f));
String outputFile = "/home/gajasurve/Desktop/done2.txt";
PrintWriter pw = new PrintWriter(new FileWriter(outputFile));
while((str = lr.readLine()) != null) {
if(str.contains(Key)) {
pw.println(str.replaceAll(Key, d2));
} else {
pw.println(str);
}
}
pw.close();
break;
}
}
}
}
那么我该怎么解决呢?为什么不在一个变量编辑的答案中的if块中指定str值,如果它解决了你的问题,就接受这个答案,否则就把你的疑问添加为注释。我们不能只将
str
的值赋给一个变量,因为可能会出现多次。我们需要一个列表来存储所有这些内容。@Codi我不明白为什么我们不能?@theRoot说我们正在寻找键
=“hello”,该文件有两行,分别包含“hello world 1”和“hello world 2”,如果我们将str
存储在变量Saystorage
,那么第一次它会存储“hello world 1”,但当“hello world 2”也被解读为正数,然后它将通过在其中存储“hello world 2”来覆盖存储
。在这种情况下,我们将丢失以前必须替换的值,因此我们需要使用列表来存储所有事件。