编程珠玑-chapter1-磁盘文件排序

FileBitSort.java

public class FileBitSort {
    public static void generateData(String path, int max) throws Exception {
        File f = new File(path);
        if (f.exists()) {
            
            f.delete();
            
        } else {
            f.createNewFile();
        }
        
        List<Long> data = new ArrayList<Long>();
        for (long i = 0; i < max; i++) {
            data.add(i);
        }
        
        Collections.shuffle(data);
        
        PrintWriter pw = null;
        try {
            pw = new PrintWriter(f);
            for (Long d : data) {
                pw.println(d);
            }
        } finally {
            if (pw != null) pw.close();
        }
    }
    
    public static void sort(String input, String output, int num) throws Exception {
        long step1 =  System.currentTimeMillis();
        //step 1: init
        byte[] data = new byte[num];
        System.out.println("init cost: " + (System.currentTimeMillis() - step1));
        
        long step2 = System.currentTimeMillis();
        //step 2: input
        BufferedReader sc = null;
        try {
            sc = new BufferedReader(new FileReader(input));
            
            String r = null;
            while ((r = sc.readLine()) != null) {
                data[Integer.parseInt(r)] = 1;
            }
            
        } finally {
            if (sc != null) sc.close();
        }
        System.out.println("input cost: " + (System.currentTimeMillis() - step2));
        
        long step3 = System.currentTimeMillis();
        //step 3: output
        PrintWriter pw = null;
        try {
            pw = new PrintWriter(output);
            for (int i = 0; i < data.length; i++) {
                if (data[i] == 1) pw.println(i);
            }
        } finally {
            if (pw != null) pw.close();
        }
        System.out.println("output cost: " + (System.currentTimeMillis() - step3));
    }
    
    public static void main(String[] args) throws Exception {
        //generateData("c:/data.txt", 10000000);
        sort("c:/data.txt", "c:/data_1.txt", 10000000);
    }
}

output.txt

init cost: 16
input cost: 3312
output cost: 3328

注：step2使用Scanner时性能较差。