added uebung04 task

uebung04/chess/Queen.java

@@ -0,0 +1,40 @@
+package chess;
+
+import static java.lang.Integer.signum;
+import static java.lang.Math.abs;
+
+public class Queen extends Piece {
+  public Queen(Color color, Board board, int row, int col) {
+    super(color, board, row, col);
+  }
+
+  @Override
+  public char charRep() {
+    return getColor() == Color.white ? 'q' : 'Q';
+  }
+
+  @Override
+  public String toString() {
+    return "" + getColor() + " queen at (" + getRow() + ", " + getCol() + ")";
+  }
+
+  @Override
+  public boolean canCapture(Piece other) {
+    if (getBoard() != other.getBoard() || getColor() == other.getColor())
+      return false;
+    if (other.getRow() != getRow() &&
+        other.getCol() != getCol() &&
+        abs(other.getRow() - getRow()) != abs(other.getCol() - getCol()))
+      return false;
+    final int dr = signum(other.getRow() - getRow());
+    final int dc = signum(other.getCol() - getCol());
+    int r = getRow() + dr;
+    int c = getCol() + dc;
+    while (r != other.getRow() || c != other.getCol()) {
+      if (getBoard().pieceAt(r, c) != null) return false;
+      r += dr;
+      c += dc;
+    }
+    return true;
+  }
+}