java:immutable-objects
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java:immutable-objects [2023/04/08 01:46] – odefta | java:immutable-objects [2023/07/04 19:36] (current) – external edit 127.0.0.1 | ||
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===== Example of immutable class ===== | ===== Example of immutable class ===== | ||
- | |||
<code java> | <code java> | ||
+ | import java.util.ArrayList; | ||
+ | import java.util.List; | ||
+ | |||
final class Record { | final class Record { | ||
- | | + | |
- | private final String name; | + | private final String name; |
- | private final List< | + | private final List< |
+ | |||
+ | public Record(long id, String name, List< | ||
+ | this.id = id; | ||
+ | this.name = name; | ||
+ | |||
+ | /* This works, but: | ||
+ | - it will always duplicate elements | ||
+ | - the same copy should be used also in getTokens() method. | ||
+ | */ | ||
+ | // | ||
+ | |||
+ | /* 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); | ||
+ | } | ||
+ | |||
+ | public long getId() { | ||
+ | return id; | ||
+ | } | ||
+ | |||
+ | 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< | ||
+ | //return new ArrayList<> | ||
+ | return tokens; | ||
+ | } | ||
+ | |||
+ | @Override | ||
+ | public String toString() { | ||
+ | return " | ||
+ | } | ||
+ | } | ||
+ | |||
+ | class TestRecord { | ||
+ | |||
+ | public static void main(String[] args) { | ||
+ | List< | ||
+ | tokens.add(" | ||
+ | tokens.add(" | ||
- | public | + | Record record = new Record(1, " |
- | this.id = id; | + | |
- | this.name = name; | + | |
- | this.tokens = tokens; | + | |
- | } | + | |
- | public long getId() { | + | tokens.remove(0); |
- | return id; | + | |
- | } | + | |
- | public String getName() { | + | System.out.println(record.withName(" |
- | return name; | + | |
- | } | + | |
- | public List< | + | record.getTokens().add("Token 3"); |
- | return new ArrayList<> | + | |
- | } | + | |
- | @Override | + | |
- | public String toString() { | + | |
- | return " | + | |
- | " | + | |
- | ", name='" | + | |
- | ", tokens=" | + | |
- | ' | + | |
- | | + | |
} | } | ||
+ | </ | ||
+ | Output: | ||
+ | < | ||
+ | Record (id = 1, name=' | ||
+ | Record (id = 1, name=' | ||
+ | Record (id = 1, name=' | ||
+ | Exception in thread " | ||
+ | at java.base/ | ||
+ | at java.base/ | ||
+ | at ro.medjava.immutability.TestRecord.main(Record.java: | ||
</ | </ | ||
java/immutable-objects.1680907604.txt.gz · Last modified: 2023/07/04 19:36 (external edit)