examplehub · realDuYuanChao · Oct 31, 2020 · Oct 31, 2020 · Oct 31, 2020 · Oct 31, 2020
diff --git a/src/main/java/com/examplehub/datastructures/stack/ExpressionEvaluation.java b/src/main/java/com/examplehub/datastructures/stack/ExpressionEvaluation.java
@@ -0,0 +1,19 @@
+package com.examplehub.datastructures.stack;
+
+import com.examplehub.strings.RemoveWhiteSpace;
+
+public class ExpressionEvaluation {
+
+  /**
+   * Expression evaluation algorithms.
+   *
+   * @param expression the expression to be calculated.
+   * @return result of expression.
+   * @throws Exception if {@code expression} is invalid.
+   */
+  public static int evaluate(String expression) throws Exception {
+
+    return PostfixEvaluation.evaluate(
+        Infix2Postfix.infix2PostFix(RemoveWhiteSpace.removeWhitespace(expression)));
+  }
+}
diff --git a/src/main/java/com/examplehub/datastructures/stack/Infix2Postfix.java b/src/main/java/com/examplehub/datastructures/stack/Infix2Postfix.java
@@ -3,6 +3,14 @@
 import java.util.Stack;
 
 public class Infix2Postfix {
+
+  /**
+   * Convert infix to postfix.
+   *
+   * @param infixExpression the infix expression.
+   * @return postfix expression.
+   * @throws Exception if infix expression is invalid.
+   */
   public static String infix2PostFix(String infixExpression) throws Exception {
     if (!BalancedParentheses.isBalanced(infixExpression)) {
       throw new Exception("invalid expression");

diff --git a/src/main/java/com/examplehub/strings/RemoveWhiteSpace.java b/src/main/java/com/examplehub/strings/RemoveWhiteSpace.java
@@ -0,0 +1,14 @@
+package com.examplehub.strings;
+
+public class RemoveWhiteSpace {
+
+  /**
+   * Remove all whitespace of a string.
+   *
+   * @param s the string to be removed whitespace.
+   * @return string no whitespace.
+   */
+  public static String removeWhitespace(String s) {
+    return s.replaceAll(" ", "");
+  }
+}
diff --git a/src/test/java/com/examplehub/datastructures/stack/ExpressionEvaluationTest.java b/src/test/java/com/examplehub/datastructures/stack/ExpressionEvaluationTest.java
@@ -0,0 +1,18 @@
+package com.examplehub.datastructures.stack;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class ExpressionEvaluationTest {
+
+  @Test
+  void evaluate() throws Exception {
+    assertEquals(5, 2 + 3);
+    assertEquals(-1, 2 - 3);
+    assertEquals(0, 2 / 3);
+    assertEquals(6, 2 * 3);
+    assertEquals(80, ExpressionEvaluation.evaluate("1+(2*3^4)/2-2"));
+    assertEquals(80, ExpressionEvaluation.evaluate("1 + (2 * 3 ^ 4) / 2 - 2"));
+  }
+}
diff --git a/src/test/java/com/examplehub/strings/RemoveWhiteSpaceTest.java b/src/test/java/com/examplehub/strings/RemoveWhiteSpaceTest.java
@@ -0,0 +1,16 @@
+package com.examplehub.strings;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class RemoveWhiteSpaceTest {
+  @Test
+  void testRemoveWhitespace() {
+    assertEquals("ILoveJava", RemoveWhiteSpace.removeWhitespace("I Love Java"));
+    assertEquals("ILoveJava", RemoveWhiteSpace.removeWhitespace("I      Love       Java"));
+    assertEquals(
+        "ILoveJava", RemoveWhiteSpace.removeWhitespace("   I      L   ov   e       Ja  va"));
+    assertEquals("", RemoveWhiteSpace.removeWhitespace("         "));
+  }
+}