chore: organize homework into first-part directory

first-part/hw-01/src/ImmutableClass.java

@@ -0,0 +1,27 @@
+import java.util.Objects;
+
+final class ImmutableClass {
+  ImmutableClass(MutableClass firstField, String secondField, Integer thirdField) {
+    this.firstField = new MutableClass(Objects.requireNonNull(firstField));
+    this.secondField = secondField;
+    this.thirdField = thirdField;
+  }
+
+  public MutableClass getFirstField() {
+    return new MutableClass(firstField);
+  }
+
+  public String getSecondField() {
+    // Копировать не нужно так как String является Immutable
+    return secondField;
+  }
+
+  public Integer getThirdField() {
+    // Копировать не нужно так как Integer является Immutable
+    return thirdField;
+  }
+
+  private final MutableClass firstField;
+  private final String secondField;
+  private final Integer thirdField;
+}