[BAEL-6363_nextInt-vs-nextLine] Integer.parseInt(scanner.nextLine()) vs scanner.nextInt() in Java (#13858)

core-java-modules/core-java-io-apis-2/src/test/java/com/baeldung/scanner/NextLineVsNextIntUnitTest.java

@@ -0,0 +1,85 @@
+package com.baeldung.scanner;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.InputMismatchException;
+import java.util.Scanner;
+
+import org.junit.jupiter.api.Test;
+
+public class NextLineVsNextIntUnitTest {
+
+    @Test
+    void whenInputLineIsNumber_thenNextLineAndNextIntBothWork() {
+        String input = "42\n";
+
+        //nextLine()
+        Scanner sc1 = new Scanner(input);
+        int num1 = Integer.parseInt(sc1.nextLine());
+        assertEquals(42, num1);
+
+        //nextInt()
+        Scanner sc2 = new Scanner(input);
+        int num2 = sc2.nextInt();
+        assertEquals(42, num2);
+
+    }
+
+    @Test
+    void whenInputIsNotValidNumber_thenNextLineAndNextIntThrowDifferentException() {
+        String input = "Nan\n";
+
+        //nextLine() -> NumberFormatException
+        Scanner sc1 = new Scanner(input);
+        assertThrows(NumberFormatException.class, () -> Integer.parseInt(sc1.nextLine()));
+
+        //nextInt() -> InputMismatchException
+        Scanner sc2 = new Scanner(input);
+        assertThrows(InputMismatchException.class, sc2::nextInt);
+    }
+
+    @Test
+    void whenUsingNextInt_thenTheNextTokenAfterItFailsToParseIsNotConsumed() {
+        String input = "42 is a magic number\n";
+
+        //nextInt() to read '42'
+        Scanner sc2 = new Scanner(input);
+        int num2 = sc2.nextInt();
+        assertEquals(42, num2);
+
+        // call nextInt() again on "is"
+        assertThrows(InputMismatchException.class, sc2::nextInt);
+
+        String theNextToken = sc2.next();
+        assertEquals("is", theNextToken);
+
+        theNextToken = sc2.next();
+        assertEquals("a", theNextToken);
+    }
+
+    @Test
+    void whenReadingTwoInputLines_thenNextLineAndNextIntBehaveDifferently() {
+
+        String input = new StringBuilder().append("42\n")
+          .append("It is a magic number.\n")
+          .toString();
+
+        //nextLine()
+        Scanner sc1 = new Scanner(input);
+        int num1 = Integer.parseInt(sc1.nextLine());
+        String nextLineText1 = sc1.nextLine();
+        assertEquals(42, num1);
+        assertEquals("It is a magic number.", nextLineText1);
+
+        //nextInt()
+        Scanner sc2 = new Scanner(input);
+        int num2 = sc2.nextInt();
+        assertEquals(42, num2);
+
+        // nextInt() leaves the newline character (\n) behind
+        String nextLineText2 = sc2.nextLine();
+        assertEquals("", nextLineText2);
+    }
+
+}