Revise README with Java example for compression

Updated usage section with a complete Java example demonstrating the compression and uncompression process using FastPFOR128.

Author: lemire

README.md

@@ -48,13 +48,50 @@ as well as in GMAP and GSNAP (http://research-pub.gene.com/gmap/).
 Usage
 ------
 
-Really simple usage:
 
 ```java
-        IntegratedIntCompressor iic = new IntegratedIntCompressor();
-        int[] data = ... ; // to be compressed
-        int[] compressed = iic.compress(data); // compressed array
-        int[] recov = iic.uncompress(compressed); // equals to data
+package org.example;
+
+import me.lemire.integercompression.FastPFOR128;
+import me.lemire.integercompression.IntWrapper;
+
+import java.util.Arrays;
+
+public class Main {
+    public static void main(String[] args) {
+        FastPFOR128 fastpfor = new FastPFOR128();
+
+        int N = 9984;
+        int[] data = new int[N];
+        for (var i = 0; i < N; i += 150) {
+            data[i] = i;
+        }
+
+        int[] compressedoutput1 = new int[N + 1024];
+
+        IntWrapper inputoffset1 = new IntWrapper(0);
+        IntWrapper outputoffset1 = new IntWrapper(0);
+
+        fastpfor.compress(data, inputoffset1, N, compressedoutput1, outputoffset1);
+        int compressedsize1 = outputoffset1.get();
+
+        int[] recovered1 = new int[N];
+        inputoffset1 = new IntWrapper(0);
+        outputoffset1 = new IntWrapper(0);
+        fastpfor.uncompress(compressedoutput1, outputoffset1, compressedsize1, recovered1, inputoffset1);
+
+        // quick verification: count mismatches
+        int mismatches = 0;
+        for (int i = 0; i < N; i++) {
+            if (data[i] != recovered1[i]) mismatches++;
+        }
+
+        System.out.println("N=" + N + " compressedSizeWords=" + compressedsize1 + " mismatches=" + mismatches);
+        System.out.println("first 20 original: " + Arrays.toString(Arrays.copyOf(data, 20)));
+        System.out.println("first 20 recovered: " + Arrays.toString(Arrays.copyOf(recovered1, 20)));
+    }
+}
+
 ```
 
 For more examples, see example.java or the examples folder.