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    <p>You can avoid the use of the Set as intermediate storage if you write at the same time that you read from file. You could do something like this,</p> <pre><code>import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; import java.io.PrintWriter; public class AppMain { private static final int NUMBER_REGISTERS = 10000000; private static String[] filePaths = {"filePath1", "filePaht2", "filePathN"}; private static String mergedFile = "mergedFile"; public static void main(String[] args) throws IOException { mergeFiles(filePaths, mergedFile); } private static void mergeFiles(String[] filePaths, String mergedFile) throws IOException{ BufferedReader[] readerArray = createReaderArray(filePaths); boolean[] closedReaderFlag = new boolean[readerArray.length]; PrintWriter writer = createWriter(mergedFile); int currentReaderIndex = 0; int numberLinesInMergedFile = 0; BufferedReader currentReader = null; String currentLine = null; while(numberLinesInMergedFile &lt; NUMBER_REGISTERS &amp;&amp; getNumberReaderClosed(closedReaderFlag) &lt; readerArray.length){ currentReaderIndex = (currentReaderIndex + 1) % readerArray.length; if(closedReaderFlag[currentReaderIndex]){ continue; } currentReader = readerArray[currentReaderIndex]; currentLine = currentReader.readLine(); if(currentLine == null){ currentReader.close(); closedReaderFlag[currentReaderIndex] = true; continue; } writer.println(currentLine); numberLinesInMergedFile++; } writer.close(); for(int index = 0; index &lt; readerArray.length; index++){ if(!closedReaderFlag[index]){ readerArray[index].close(); } } } private static BufferedReader[] createReaderArray(String[] filePaths) throws FileNotFoundException{ BufferedReader[] readerArray = new BufferedReader[filePaths.length]; for (int index = 0; index &lt; readerArray.length; index++) { readerArray[index] = createReader(filePaths[index]); } return readerArray; } private static BufferedReader createReader(String path) throws FileNotFoundException{ BufferedReader reader = new BufferedReader(new FileReader(path)); return reader; } private static PrintWriter createWriter(String path) throws FileNotFoundException{ PrintWriter writer = new PrintWriter(path); return writer; } private static int getNumberReaderClosed(boolean[] closedReaderFlag){ int count = 0; for (boolean currentFlag : closedReaderFlag) { if(currentFlag){ count++; } } return count; } } </code></pre>
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    1. POMerge the files into a new big file until the number of user id's become 10 Million
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    1. USJuan Jose Fidalgo
    1. USJuan Jose Fidalgo
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    1. This table or related slice is empty.
 

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