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java:immutable-objects [2023/04/08 02:26] – odeftajava:immutable-objects [2023/04/08 02:38] – odefta
Line 23: Line 23:
  
 ===== Example of immutable class ===== ===== Example of immutable class =====
- 
 <code java> <code java>
 import java.util.ArrayList; import java.util.ArrayList;
Line 37: Line 36:
         this.id = id;         this.id = id;
         this.name = name;         this.name = name;
-        /*  This works, but it will always 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);         //this.tokens = new ArrayList<>(tokens);
 +
         /*  If tokens is already unmodifiable (for ex. was formed using List.of),         /*  If tokens is already unmodifiable (for ex. was formed using List.of),
             then it will not duplicate elements.             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);         this.tokens = List.copyOf(tokens);
Line 63: Line 69:
  
     public List<String> getTokens() {     public List<String> getTokens() {
 +        //return new ArrayList<>(tokens);
         return tokens;         return tokens;
     }     }
Line 68: Line 75:
     @Override     @Override
     public String toString() {     public String toString() {
-        return "Record (id = " + id + ", name='" + name + '\'' + ", tokens=" + tokens + ')';+        return "Record (id = " + id + ", name='" + name + '\'' + ", tokens=" + tokens + ")";
     }     }
 } }
Line 92: Line 99:
     }     }
 } }
 +</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> </code>
  
java/immutable-objects.txt · Last modified: 2023/07/04 19:36 by 127.0.0.1