IntOperator implementation with evaluation and argument count checking.

Co-Authored-By: td1223

src/main/java/ic/doc/IntOperator.java

@@ -0,0 +1,23 @@
+package ic.doc;
+
+import java.util.List;
+import java.util.function.Function;
+
+public class IntOperator {
+  private final int operands;
+  private final Function<List<Integer>, Integer> operator;
+
+  IntOperator(int operands, Function<List<Integer>, Integer> operator) {
+    this.operands = operands;
+    this.operator = operator;
+  }
+
+  public int evaluate(List<Integer> arguments) {
+    if (arguments.size() != operands) {
+      throw new IllegalArgumentException(
+        String.format("Expected %d arguments, got %d", operands, arguments.size())
+      );
+    }
+    return operator.apply(arguments);
+  }
+}

src/test/java/ic/doc/IntOperatorTest.java

@@ -0,0 +1,28 @@
+package ic.doc;
+
+import org.junit.Test;
+
+import java.util.List;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.fail;
+
+public class IntOperatorTest {
+  @Test
+  public void intOperatorCanEvaluate() {
+    IntOperator intOperator = new IntOperator(2, arguments -> arguments.get(0) + arguments.get(1));
+    assertThat(intOperator.evaluate(List.of(1, 2)), is(3));
+  }
+
+  @Test
+  public void intOperatorThrowsOnInvalidArguments() {
+    IntOperator intOperator = new IntOperator(2, arguments -> arguments.get(0) + arguments.get(1));
+    try {
+      intOperator.evaluate(List.of(1));
+      fail("Expected IllegalArgumentException to be thrown on invalid number of arguments");
+    } catch (IllegalArgumentException e) {
+      // good
+    }
+  }
+}