[store-triple-in-list] Storing Data Triple in a List in Java (#13295)

* [store-triple-in-list] Storing Data Triple in a List in Java

* [store-triple-in-list] method name "give..."->"given..."

core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/triple/Triple.java

@@ -0,0 +1,26 @@
+package com.baeldung.triple;
+
+public class Triple<L, M, R> {
+
+    private final L left;
+    private final M middle;
+    private final R right;
+
+    public Triple(L left, M middle, R right) {
+        this.left = left;
+        this.middle = middle;
+        this.right = right;
+    }
+
+    public L getLeft() {
+        return left;
+    }
+
+    public M getMiddle() {
+        return middle;
+    }
+
+    public R getRight() {
+        return right;
+    }
+}

core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/triple/TripleInListUnitTest.java

@@ -0,0 +1,105 @@
+package com.baeldung.triple;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import org.junit.jupiter.api.Test;
+
+public class TripleInListUnitTest {
+
+    enum OP {
+        PLUS("+"), MINUS("-"), MULTIPLY("x");
+        final String opSign;
+
+        OP(String x) {
+            this.opSign = x;
+        }
+    }
+
+    private String createQuestion(Long num1, OP operator, Long num2) {
+        long result;
+        switch (operator) {
+            case PLUS:
+                result = num1 + num2;
+                break;
+            case MINUS:
+                result = num1 - num2;
+                break;
+            case MULTIPLY:
+                result = num1 * num2;
+                break;
+            default:
+                throw new IllegalArgumentException("Unknown operator");
+        }
+        return String.format("%d %s %d = ? ( answer: %d )", num1, operator.opSign, num2, result);
+    }
+
+    private static final List<String> EXPECTED_QUESTIONS = Arrays.asList(
+        "100 - 42 = ? ( answer: 58 )",
+        "100 + 42 = ? ( answer: 142 )",
+        "100 x 42 = ? ( answer: 4200 )");
+
+    @Test
+    void givenTripleValues_whenStoreAsList_thenTypeIsNotSafe() {
+
+        List myTriple1 = new ArrayList(3);
+        myTriple1.add(100L);
+        myTriple1.add(OP.MINUS);
+        myTriple1.add(42L);
+
+        List myTriple2 = new ArrayList(3);
+        myTriple2.add(100L);
+        myTriple2.add(OP.PLUS);
+        myTriple2.add(42L);
+
+        List myTriple3 = new ArrayList(3);
+        myTriple3.add(100L);
+        myTriple3.add(OP.MULTIPLY);
+        myTriple3.add(42L);
+
+        List<List> listOfTriples = new ArrayList<>(Arrays.asList(myTriple1, myTriple2, myTriple3));
+
+        List oopsTriple = new ArrayList(3);
+        oopsTriple.add("Oops");
+        oopsTriple.add(911L);
+        oopsTriple.add("The type is wrong");
+
+        listOfTriples.add(oopsTriple);
+        assertEquals(4, listOfTriples.size());
+
+        List<String> questions = listOfTriples.stream()
+            .filter(
+                triple -> triple.size() == 3
+                    && triple.get(0) instanceof Long
+                    && triple.get(1) instanceof OP
+                    && triple.get(2) instanceof Long
+            ).map(triple -> {
+                Long left = (Long) triple.get(0);
+                OP op = (OP) triple.get(1);
+                Long right = (Long) triple.get(2);
+                return createQuestion(left, op, right);
+            }).collect(Collectors.toList());
+
+        assertEquals(EXPECTED_QUESTIONS, questions);
+    }
+
+    @Test
+    void givenTripleValues_whenUsingTheTripleClass_thenTypeIsSafeAndNeat() {
+        Triple<Long, OP, Long> triple1 = new Triple<>(100L, OP.MINUS, 42L);
+        Triple<Long, OP, Long> triple2 = new Triple<>(100L, OP.PLUS, 42L);
+        Triple<Long, OP, Long> triple3 = new Triple<>(100L, OP.MULTIPLY, 42L);
+        Triple<String, Long, String> tripleOops = new Triple<>("Oops", 911L, "The type is wrong");
+
+        List<Triple<Long, OP, Long>> listOfTriples = new ArrayList<>(Arrays.asList(triple1, triple2, triple3));
+        // listOfTriples.add(tripleOops); // Compiler error: "java: incompatible types ... "
+
+        List<String> questions = listOfTriples.stream()
+            .map(triple -> createQuestion(triple.getLeft(), triple.getMiddle(), triple.getRight()))
+            .collect(Collectors.toList());
+
+        assertEquals(EXPECTED_QUESTIONS, questions);
+    }
+}