Move custom set to abstraction package

4-Abstraction/src/main/java/datastructures/set/CustomSet.java

@@ -0,0 +1,17 @@
+package datastructures.set;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+public interface CustomSet<T> {
+
+
+
+	Stream<T> stream();
+
+	boolean add(T value);
+
+	boolean remove(T value);
+
+	Set<T> getSet();
+}

4-Abstraction/src/main/java/datastructures/set/CustomStrictSet.java

@@ -0,0 +1,44 @@
+package datastructures.set;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+public class CustomStrictSet<T> implements CustomSet<T> {
+
+	private final Set<T> set;
+
+	public CustomStrictSet(Set<T> set) {
+		this.set = set;
+	}
+
+	@Override
+	public Stream<T> stream() {
+		return this.set.stream();
+	}
+
+	@Override
+	public Set<T> getSet() {
+		return this.set;
+	}
+
+	@Override
+	public boolean add(T value) {
+
+		if (this.set.contains(value)) {
+			throw new ElementAlreadyInSet("Tried adding " + value + " of class " + value
+					.getClass()
+					.getName() + " but the set already contains it.");
+		}
+		return this.set.add(value);
+	}
+
+	@Override
+	public boolean remove(T value) {
+		if (!this.set.contains(value)) {
+			throw new ElementNotInSet("Tried removing " + value + " of class " + value
+					.getClass()
+					.getName() + " but the set not contains it.");
+		}
+		return this.set.remove(value);
+	}
+}

4-Abstraction/src/main/java/datastructures/set/ElementAlreadyInSet.java

@@ -0,0 +1,8 @@
+package datastructures.set;
+
+public class ElementAlreadyInSet extends RuntimeException {
+
+	public ElementAlreadyInSet(String message) {
+		super(message);
+	}
+}

4-Abstraction/src/main/java/datastructures/set/ElementNotInSet.java

@@ -0,0 +1,8 @@
+package datastructures.set;
+
+public class ElementNotInSet extends RuntimeException {
+
+	public ElementNotInSet(String message) {
+		super(message);
+	}
+}