[android] - add toString to Expression to print out object array notation

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/expressions/Expression.java

@@ -1776,4 +1776,22 @@ public class Expression<T> {
     return output;
   }
 
+
+  @Override
+  public String toString() {
+    StringBuilder builder = new StringBuilder();
+    builder.append("[\"").append(operator).append("\"");
+    if (arguments != null) {
+      for (Expression argument : arguments) {
+        builder.append(", ");
+        if (argument instanceof ExpressionLiteral) {
+          builder.append(((ExpressionLiteral) argument).toValue());
+        } else {
+          builder.append(argument.toString());
+        }
+      }
+    }
+    builder.append("]");
+    return builder.toString();
+  }
 }

platform/android/MapboxGLAndroidSDK/src/test/java/com/mapbox/mapboxsdk/style/expressions/ExpressionTest.java

@@ -76,6 +76,7 @@ import static com.mapbox.mapboxsdk.style.expressions.Expression.upcase;
 import static com.mapbox.mapboxsdk.style.expressions.Expression.var;
 import static com.mapbox.mapboxsdk.style.expressions.Expression.zoom;
 import static junit.framework.Assert.assertTrue;
+import static org.junit.Assert.assertEquals;
 
 /**
  * Expression unit tests that validate the expression output with the expected Object[]array representation.
@@ -1007,4 +1008,26 @@ public class ExpressionTest {
       literal(1)), get("x"), stop(0, 100), stop(100, 200)).toArray();
     assertTrue("expression should match", Arrays.deepEquals(expected, actual));
   }
+
+  @Test
+  public void testExpressionConcatToString() throws Exception {
+    String expected = "[\"concat\", foo, bar]";
+    String actual = concat(literal("foo"), literal("bar")).toString();
+    assertEquals("toString should match", expected, actual);
+  }
+
+  @Test
+  public void testExpressionMinToString() throws Exception {
+    String expected = "[\"min\", 0, 1, 2, 3]";
+    String actual = min(0, 1, 2, 3).toString();
+    assertEquals("toString should match", expected, actual);
+  }
+
+  @Test
+  public void testExpressionExponentialToString() throws Exception {
+    String expected = "[\"interpolate\", [\"cubic-bezier\", 1, 1, 1, 1], [\"get\", x], 0, 100, 100, 200]";
+    String actual = interpolate(cubicBezier(literal(1), literal(1), literal(1), literal(1)),
+      get(literal("x")), literal(0), literal(100), literal(100), literal(200)).toString();
+    assertEquals("toString should match", expected, actual);
+  }
 }