Pattern Matching for instanceof(2nd Preview) • Kotlinのスマートキャストのような機能 Object o = "test"; if (o instanceof String s) { System.out.println(s.length()); } Object o = "test"; if (o instanceof String) { String s = (String) o; System.out.println(s.length()); }
swtichでパターンマッチングが使えるように なると便利 • Pattern matching for switchが導入されると、次のような switchがdefaultなしで書けるようになる String getName(Shape s) { switch (s) { case Circle c -> return "円"; case Rectangle r -> return "四角"; case Square q -> return "正方形"; } }
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } recordで宣言
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } 要素(コンポーネント)を定義
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } 中かっこが必要 追加のメソッドなどの定義も可
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } 暗黙にfinal
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } java.lang.Recordを継承
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } コンポーネントに 対応するフィールド private final
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } コンストラクタが定義される
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } コンポーネントと同名の アクセスメソッド getterではない
Recordの定義 public record Rec(String name, int count) {} public final class Rec extends Record { private final String name; private final int count; Rec(String name, int count) { this.name = name; this.count = count; } String name() { return name; } String count() { return count; } // toString, equals, hashCode } オブジェクトの基本メソッドも 実装される
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