Java FileInputStream available()用法及代碼示例

FileInputStream 類的 available() 方法用於返回可以從輸入流中讀取而不會阻塞的估計剩餘字節數。此方法返回要從文件中讀取的剩餘字節數。當一個文件被完全讀取時，這個函數返回零。

用法:

FileInputStream available() 

返回值：該方法返回並估計從該輸入流中讀取的剩餘字節數而不阻塞。

異常：該方法可以產生IOException或FileNotFoundException等異常。這些異常如下所述。

• IOException -如果文件輸入流已通過調用 close 關閉或發生任何 I/O 錯誤。
• FileNotFoundException -如果該目錄不可用，那麽我們將得到 FileNotFoundException。

如何調用 available() 方法？

第 1 步：將文件附加到 FileInputStream，因為這將使我們能夠從文件中讀取數據，如下所示：

FileInputStream fileInputStream = new FileInputStream(“file.txt”);

第 2 步：現在，要從文件中讀取有多少數據可供讀取的數據，我們應該使用 FileInputStream 對象調用一個可用的方法，如下所示；

int ch = fileInputStream.available(); 

Step 3(a)：當沒有更多數據可供進一步讀取時，available()方法返回0；

步驟 3(b)：然後，我們應該將監視器附加到輸出流。為了顯示數據，我們可以使用 System.out.print。

System.out.print(ch);

Implementation

原始文件內容：file.txt

GeeksforGeeks

該程序將讀取一個文件並返回每次讀取的字符數。

// Java program to demonstrate the working
// of the FileInputStream available() method
import java.io.File;
import java.io.FileInputStream;
public class abc {
    public static void main(String[] args)
    {
        // Creating file object and specifying path
        File file = new File("file.txt");
        try {
            FileInputStream input = new FileInputStream(file);
            int character;
            // read character by character by default
            // read() function return int between 0 and 255.
            while ((character = input.read()) != -1) {
                int ch = input.available();
                System.out.print("Currently Reading:"
                                 + (char)character);
                System.out.print(" Remaining character:"
                                 + ch);
                System.out.println();
            }
            input.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

輸出

Currently Reading:G Remaining character:12
Currently Reading:e Remaining character:11
Currently Reading:e Remaining character:10
Currently Reading:k Remaining character:9
Currently Reading:s Remaining character:8
Currently Reading:f Remaining character:7
Currently Reading:o Remaining character:6
Currently Reading:r Remaining character:5
Currently Reading:G Remaining character:4
Currently Reading:e Remaining character:3
Currently Reading:e Remaining character:2
Currently Reading:k Remaining character:1
Currently Reading:s Remaining character:0