ADD file via upload

ResizableSquare.java

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+package jinjieti;
+
+import jichuti.Square;
+
+/**
+ * 可缩放的正方形（实现Shape和Resizable）
+ */
+public class ResizableSquare extends Square implements Resizable {
+    public ResizableSquare(String color, double side) {
+        super(color, side);
+    }
+
+    @Override
+    public void resize(double factor) {
+        if (factor <= 0) {
+            throw new IllegalArgumentException("缩放因子必须为正数");
+        }
+        setSide(getSide() * factor);  // 调整边长
+    }
+}