無法在java中關閉我的DataInputStream和DataOutputStream

Question

我最近開始學習java中的文件處理。然而，在這段代碼中（下面），我試圖在所有閱讀和寫作結束時關閉文件，但是以這種方式面臨錯誤。

package trycatch; 

import java.util.Scanner; 
import org.omg.CORBA.DataInputStream; 

import java.*; 
import java.io.DataOutputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.Writer; 

public class Source { 

public static void main(String[] args) throws Exception { 

    Scanner input = new Scanner(System.in); 
    try { 
    File f = new File("record.txt"); 

    FileOutputStream writing = new FileOutputStream(f); 
    DataOutputStream write = new DataOutputStream(writing); 
    write.writeUTF("What are the things that you want to do"); 

    String str; 

    FileInputStream reading = new FileInputStream(f); 
    java.io.DataInputStream read = new java.io.DataInputStream(reading); 
    str = read.readUTF(); 
    System.out.println(str); 
    } 
    catch(FileNotFoundException e) { 

     System.out.println("The system collapsed"); 
    } 
    finally { 
     write.close(); // write cannot be resolved 
     read.close(); // read cannot be resolved 
    } 

    input.close(); 
} 
} 

我想出來的終於關鍵字，但你能告訴我爲什麼我的IDE無法識別閱讀和寫當我把它寫在那裏？

寫不能得到解決

Answer 1

您聲明write在try塊內。它不能在finally塊內解析，因爲這是一個不同的範圍。

您需要在try塊之前聲明write，使之獲得在最後：

DataOutputStream write = null; 
try { 
... 
    write = new DataOutputStream(writing); 
... 
} finally { 
    if (write != null) { 
     write.close(); 
    } 
} 

隨着最新版本的Java，你可以/應該使用try-與資源結構，以確保正確的資源處理。有了這個，你可以省略最後塊當試塊留在JVM會照顧關閉您的資源：

try (DataOutputStream write = new DataOutputStream(writing)) { 
    ... 
} 

Answer 2

你的讀取和寫入領域是本地try塊，終於無法訪問然後在嘗試之外初始化它。

Answer 3

寫入和讀取在try塊中創建，它們的作用域僅在塊中。將聲明移至input並且它應該起作用。

Answer 4

試試看這樣的：

package trycatch; 

import java.util.Scanner; 
import org.omg.CORBA.DataInputStream; 

import java.*; 
import java.io.DataOutputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.Writer; 

public class Source { 

public static void main(String[] args) throws Exception { 

    Scanner input = new Scanner(System.in); 
    DataOutputStream write = null; 
    java.io.DataInputStream read = null; 
    try { 
    File f = new File("record.txt"); 

    FileOutputStream writing = new FileOutputStream(f); 
    write = new DataOutputStream(writing); 
    write.writeUTF("What are the things that you want to do"); 

    String str; 

    FileInputStream reading = new FileInputStream(f); 
    read = new java.io.DataInputStream(reading); 
    str = read.readUTF(); 
    System.out.println(str); 
    } 
    catch(FileNotFoundException e) { 

     System.out.println("The system collapsed"); 
    } 
    finally { 
     if (write != null) 
      write.close(); // write cannot be resolved 
     if (read != null) 
      read.close(); // read cannot be resolved 
    } 

    input.close(); 
} 
}