Add Java implementation

src/freq01.java

@@ -0,0 +1,88 @@
+import java.io.*;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static java.lang.Character.toLowerCase;
+
+class freq01 {
+
+    public static void main(String[] args) throws IOException {
+
+        if (args.length < 3) {
+            System.out.println("usage: freq <in.txt> <out.txt> [--prof]");
+            return;
+        }
+
+        List<String> words = new ArrayList<>();
+        try (BufferedReader fileBufferReader = new BufferedReader(new FileReader(args[1]))) {
+            String line;
+            StringBuilder sb = new StringBuilder();
+            while ((line = fileBufferReader.readLine()) != null) {
+                char[] s = line.toCharArray();
+                for (char c: s) {
+                    if (c >= 'a' && c <= 'z') {
+                        sb.append(c);
+                    } else if (c >= 'A' && c <= 'Z') {
+                        sb.append(toLowerCase(c));
+                    } else if (sb.length() > 0) {
+                        words.add(sb.toString());
+                        sb.setLength(0);
+                    }
+                }
+                if (sb.length() > 0) {
+                    words.add(sb.toString());
+                    sb.setLength(0);
+                }
+            }
+        }
+
+        List<E> res = new freq01().freq(words);
+
+        PrintWriter pw = new PrintWriter(new FileWriter(args[2]));
+        StringBuilder sb = new StringBuilder();
+        for (E e: res) {
+            sb.setLength(0);
+            pw.println(sb.append(e.freq).append(" ").append(e.s));
+        }
+        pw.close();
+    }
+
+    public List<E> freq(List<String> words) {
+        Map<String, E> m = new HashMap<>(words.size() >> 2);
+        for (String word: words) {
+            m.compute(word, freq01::update);
+        }
+
+        return m.values()
+                .stream()
+                .sorted()
+                .collect(Collectors.toList());
+    }
+
+    static E update(String k, E v) {
+        if (v != null) {
+            v.freq++;
+            return v;
+        } else {
+            return new E(k);
+        }
+    }
+
+    static class E implements Comparable<E> {
+        final String s;
+        int freq;
+
+        E(String s) {
+            this.s = s;
+            this.freq = 1;
+        }
+
+        @Override
+        public int compareTo(E other) {
+            return freq != other.freq ? other.freq - freq : s.compareTo(other.s);
+        }
+    }
+}