update collection (#198)

Author: realDuYuanChao

src/main/java/com/examplehub/basics/collection/CollectionExample.java

@@ -0,0 +1,4 @@
+package com.examplehub.basics.collection;
+
+public class CollectionExample {
+}

src/test/java/com/examplehub/basics/collection/CollectionExampleTest.java

@@ -0,0 +1,151 @@
+package com.examplehub.basics.collection;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CollectionExampleTest {
+
+  @Test
+  void testRemove() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+    assertTrue(collection.remove("1"));
+    assertTrue(collection.remove("4"));
+    assertFalse(collection.remove("5"));
+    assertEquals("[2, 3]", collection.toString());
+  }
+
+  @Test
+  void testRemoveAll() {
+    Collection<String> c1 = new ArrayList<>();
+    c1.add("1");
+    c1.add("2");
+    c1.add("3");
+    c1.add("4");
+
+    Collection<String> c2 = new ArrayList<>();
+    c2.add("2");
+    c2.add("3");
+    c2.add("5");
+
+    assertTrue(c1.removeAll(c2));
+    assertEquals("[1, 4]", c1.toString());
+    assertEquals("[2, 3, 5]", c2.toString());
+  }
+
+  @Test
+  void testRetainAll() {
+    Collection<String> c1 = new ArrayList<>();
+    c1.add("1");
+    c1.add("2");
+    c1.add("3");
+    c1.add("4");
+
+    Collection<String> c2 = new ArrayList<>();
+    c2.add("2");
+    c2.add("4");
+    c2.add("5");
+
+    assertTrue(c1.retainAll(c2));
+    assertEquals("[2, 4]", c1.toString());
+  }
+
+  @Test
+  void testToArray() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+    Object[] objects = collection.toArray();
+    assertEquals("[1, 2, 3, 4]", Arrays.toString(objects));
+  }
+
+  @Test
+  void testConvertArrayToCollection() {
+    String[] digits = {"1", "2", "3", "4"};
+    Collection<String> collection = Arrays.asList(digits);
+    assertEquals("[1, 2, 3, 4]", collection.toString());
+  }
+
+  @Test
+  void testIterator() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+
+    Iterator<String> iterator = collection.iterator();
+    int count = 1;
+    while (iterator.hasNext()) {
+      assertEquals(count++ + "", iterator.next());
+    }
+  }
+
+  @Test
+  void testWriteToString() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+
+    Iterator<String> iterator = collection.iterator();
+    StringBuilder builder = new StringBuilder();
+    if (!iterator.hasNext()) {
+      builder.append("[]");
+    } else {
+      builder.append("[");
+      while (iterator.hasNext()) {
+        String curItem = iterator.next();
+        if (iterator.hasNext()) {
+          builder.append(curItem).append(", ");
+        } else {
+          builder.append(curItem).append("]");
+        }
+      }
+    }
+    assertEquals("[1, 2, 3, 4]", builder.toString());
+  }
+
+  @Test
+  void testRemoveUsingIterator() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+
+    Iterator<String> iterator = collection.iterator();
+    while (iterator.hasNext()) {
+      iterator.next();
+      iterator.remove();
+    }
+    assertEquals("[]", collection.toString());
+  }
+
+
+  @Test
+  void testForEach() {
+    Collection<String> collection = new ArrayList<>();
+    collection.add("1");
+    collection.add("2");
+    collection.add("3");
+    collection.add("4");
+
+    int count = 1;
+    for (String item : collection) {
+      assertEquals(count++ + "", item);
+    }
+  }
+}