Adds setByteAt

Author: patrickfav

README.md

@@ -440,6 +440,7 @@ MutableBytes b = Bytes.from(array).mutable();
 Mutable classes also enable further APIs for directly modify the internal array:
 
 ```java
+b.setByteAt(3, (byte) 0xF1)
 b.overwrite(anotherArray) //directly overwrite given array
 b.fill(0x03) // fills with e.g. 3
 b.wipe() //fills with zeros

src/main/java/at/favre/lib/bytes/MutableBytes.java

@@ -31,6 +31,7 @@
  * <p>
  * Adds additional mutator, which may change the internal array in-place, like {@link #wipe()}
  */
+@SuppressWarnings("WeakerAccess")
 public final class MutableBytes extends Bytes {
 
     MutableBytes(byte[] byteArray, ByteOrder byteOrder) {
@@ -68,6 +69,18 @@ public MutableBytes overwrite(byte[] newArray, int offsetInternalArray) {
         return this;
     }
 
+    /**
+     * Sets new byte to given index
+     *
+     * @param index   the index to change
+     * @param newByte the new byte to set
+     * @return this instance
+     */
+    public MutableBytes setByteAt(int index, byte newByte) {
+        internalArray()[index] = newByte;
+        return this;
+    }
+
     /**
      * Fills the internal byte array with all zeros
      *

src/test/java/at/favre/lib/bytes/MutableBytesABytesTest.java

@@ -68,6 +68,19 @@ public void fill() throws Exception {
         assertArrayEquals(new byte[example_bytes_seven.length], b.array());
     }
 
+    @Test
+    public void setByteAtTest() throws Exception {
+        MutableBytes b = fromAndTest(example_bytes_sixteen).mutable();
+
+        for (int i = 0; i < b.length(); i++) {
+            byte old = b.byteAt(i);
+            b.setByteAt(i, (byte) 0);
+            if (old != 0) {
+                assertNotEquals(old, b.byteAt(i));
+            }
+        }
+    }
+
     @Test
     public void wipe() throws Exception {
         MutableBytes b = fromAndTest(example_bytes_seven).mutable();