Differences

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--- java:immutable-objects [2023/04/08 02:16] – odefta
+++ java:immutable-objects [2023/04/08 02:38] – odefta
@@ Line 23: / Line 23: @@
 ===== Example of immutable class =====
 <code java>
 import java.util.ArrayList;
@@ Line 37: / Line 36: @@
         this.id = id;
         this.name = name;
-        //this.tokens = new ArrayList<>(tokens); //this works, but it will always duplicate elements
-        this.tokens = List.copyOf(tokens); //if tokens is already unmodifiable (for ex. came from List.of) it will not duplicate elements.
+        /*  This works, but:
+         - it will always duplicate elements
+         - the same copy should be used also in getTokens() method.
+        */
+        //this.tokens = new ArrayList<>(tokens);
+        /*  If tokens is already unmodifiable (for ex. was formed using List.of),
+            then it will not duplicate elements.
+            Also, it will prevent the tokens to be modified
+            (it will throw java.lang.UnsupportedOperationException).
+         */
+        this.tokens = List.copyOf(tokens);
     }
@@ Line 47: / Line 57: @@
     public String getName() {
         return name;
+    }
+    /**
+     * No simple setters, return another copy of the object.
+     * @param name
+     * @return Record
+     */
+    public Record withName(String name) {
+        return new Record(id, name, tokens);
     }
     public List<String> getTokens() {
+        //return new ArrayList<>(tokens);
         return tokens;
     }
@@ Line 55: / Line 75: @@
     @Override
     public String toString() {
-        return "Record (id = " + id + ", name='" + name + '\'' + ", tokens=" + tokens + ')';
+        return "Record (id = " + id + ", name='" + name + '\'' + ", tokens=" + tokens + ")";
     }
 }
@@ Line 70: / Line 90: @@
         tokens.remove(0);
+        System.out.println(record);
+        System.out.println(record.withName("Two"));
+        record.getTokens().add("Token 3");
         System.out.println(record);
     }
 }
+</code>
+Output:
+<code>
+Record (id = 1, name='One', tokens=[Token 1, Token 2])
+Record (id = 1, name='One', tokens=[Token 1, Token 2])
+Record (id = 1, name='Two', tokens=[Token 1, Token 2])
+Exception in thread "main" java.lang.UnsupportedOperationException
+	at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:71)
+	at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:75)
+	at ro.medjava.immutability.TestRecord.main(Record.java:65)
 </code>