[rm-char-in-other-str] BAEL-7355 Remove characters from a string that… (#15531)

* [rm-char-in-other-str] BAEL-7355 Remove characters from a string that are present in a second string

* [rm-char-in-other-str] shorten the package name

core-java-modules/core-java-string-algorithms-4/src/test/java/com/baeldung/string/rmcharsinanotherstring/RemoveCharsInAnotherStringUnitTest.java

@@ -0,0 +1,75 @@
+package com.baeldung.string.rmcharsinanotherstring;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.jupiter.api.Test;
+
+public class RemoveCharsInAnotherStringUnitTest {
+
+    private static final String STRING = "a b c d e f g h i j";
+    private static final String OTHER = "bdfhj";
+
+    String nestedLoopApproach(String theString, String other) {
+        StringBuilder sb = new StringBuilder();
+        for (char c : theString.toCharArray()) {
+            boolean found = false;
+            for (char o : other.toCharArray()) {
+                if (c == o) {
+                    found = true;
+                    break;
+                }
+            }
+            if (!found) {
+                sb.append(c);
+            }
+        }
+        return sb.toString();
+    }
+
+    String loopAndIndexOfApproach(String theString, String other) {
+        StringBuilder sb = new StringBuilder();
+        for (char c : theString.toCharArray()) {
+            if (other.indexOf(c) == -1) {
+                sb.append(c);
+            }
+        }
+        return sb.toString();
+    }
+
+    String hashSetApproach(String theString, String other) {
+        StringBuilder sb = new StringBuilder();
+        Set<Character> set = new HashSet<>(other.length());
+        for (char c : other.toCharArray()) {
+            set.add(c);
+        }
+
+        for (char i : theString.toCharArray()) {
+            if (!set.contains(i)) {
+                sb.append(i);
+            }
+        }
+        return sb.toString();
+    }
+
+    @Test
+    void whenUsingTheNestedLoopApproach_thenGetExpectedResult() {
+        String result = nestedLoopApproach(STRING, OTHER);
+        assertEquals("a  c  e  g  i ", result);
+    }
+
+    @Test
+    void whenUsingTheLoopAndIndexOfApproach_thenGetExpectedResult() {
+        String result = loopAndIndexOfApproach(STRING, OTHER);
+        assertEquals("a  c  e  g  i ", result);
+    }
+
+    @Test
+    void whenUsingTheHashSetApproach_thenGetExpectedResult() {
+        String result = hashSetApproach(STRING, OTHER);
+        assertEquals("a  c  e  g  i ", result);
+    }
+
+}