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[英]Who is better in performance filechannel or RandomAccessFile for reading and writing?
[英]randomAccessFile method not writing or reading ints?
我有兩種方法,一種是將10個整數寫入randomAccessFile,另一種是讀取10個整數。 我相信writer方法無法正常運行。
這是我寫入隨機文件的方法:
try{
RandomAccessFile file = new RandomAccessFile(nextPath, "rw");
System.out.println("Writing these ints to file");
file.seek(0);
// here I loop 10 times and write the int at position i
for (int i = 0; i < 10; i++)
{
file.seek(i);
toAdd = randInt(1,10);
file.writeInt(toAdd);
System.out.printf(toAdd + " ");
}
file.seek(0);
System.out.println("");
}catch(IOException ex){
System.out.println("Error");
System.exit(0);}
這是我讀取int的方法:
public int[] readRandom()
{
System.out.println("Unsorted ints found in random file:");
int[] randomInts = new int[10];
try{
RandomAccessFile file = new RandomAccessFile(nextPath, "rw");
file.seek(0);
// here I loop 10 times, and read the Int at position i
for(int i = 0; i < 10; i++)
{
file.seek(i);
randomInts[i] = file.readInt();
System.out.printf(randomInts[i] + " ");
}
file.seek(0);
System.out.println("");
}catch(IOException exc){
System.out.println("Error reading ints");
System.exit(0);}
return randomInts;
}
這是我的輸出:為什么只讀取最后一個int?
Writing these ints to file
1 4 5 6 2 4 10 6 5 5
Unsorted ints found in random file:
0 0 0 0 0 0 0 0 0 5
在執行file.seek(i)時,您錯過了重要的一點。 seek()方法將查找您提供的字節位置,並且將要查找的位置增加1。但是,當您將整數寫入文件時,它將為每個整數寫入4個字節。 你的櫃台應該是這樣
for (int i = 0; i < 10; i++) {
file.seek(i*4);
toAdd = randInt(1,10);
file.writeInt(toAdd);
System.out.printf(toAdd + " ");
}
顯然,對於閱讀,您可以執行此操作
for (int i = 0; i < 10; i++)
{
file.seek(i*4);
randomInts[i] = file.readInt();
System.out.printf(randomInts[i] + " ");
}
為什么要使用RandomAccessFile
執行順序寫入和順序讀取? 它違背了這個階級的目的。
此外,您不應震驚捕獲的異常,而應記錄或跟蹤它們。
關於您的意外結果,這是由不必要的seek()
調用引起的。 您不需要在每次讀取或寫入操作時都調用seek()
,因為readInt()
和writeInt()
可使光標前進。
我已經簡化了示例代碼以強調重要部分:
public void write() {
try {
RandomAccessFile file = new RandomAccessFile("temp.txt", "rw");
System.out.println("Writing these ints to file");
file.seek(0);
for (int i = 0; i < 10; i++) {
file.writeInt(i);
System.out.printf(i + " ");
}
} catch (IOException ex) {
ex.printStackTrace();
System.exit(0);
}
}
public int[] readRandom() {
System.out.println("Unsorted ints found in random file:");
int[] randomInts = new int[10];
try {
RandomAccessFile file = new RandomAccessFile("temp.txt", "rw");
long filePointer = file.getFilePointer();
file.seek(0);
for (int i=0; i<10; i++){
randomInts[i] = file.readInt();
System.out.printf(randomInts[i] + " ");
}
} catch (IOException ex) {
ex.printStackTrace();
System.exit(0);
}
return randomInts;
}
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