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Language Intermediate

Flexible constructor bodies

Validate and compute values before calling super() or this().

Code Comparison

✕ Java 8

class Square extends Shape {
    Square(double side) {
        super(side, side);
        // can't validate BEFORE super!
        if (side <= 0)
            throw new IAE("bad");
    }
}

✓ Java 25+

class Square extends Shape {
    Square(double side) {
        if (side <= 0)
            throw new IAE("bad");
        super(side, side);
    }
}

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Why the modern way wins

🛡️

Fail fast

Validate arguments before the superclass constructor runs.

🧮

Compute first

Derive values and prepare data before calling super().

🧹

No workarounds

No more static helper methods or factory patterns to work around the restriction.

Old Approach

Validate After super()

Modern Approach

Code Before super()

Since JDK

Difficulty

Intermediate

JDK Support

Flexible constructor bodies

Available

Finalized in JDK 25 LTS (JEP 513, Sept 2025).

How it works

Java 25 lifts the restriction that super() must be the first statement. You can now validate arguments, compute derived values, and set up state before delegating to the parent constructor.

Type inference with var

Java 8

Map<String, List<Integer>> map =
    new HashMap<String, List<Integer>>();
for (Map.Entry<String, List<Integer>> e
    : map.entrySet()) {
    // verbose type noise
}

Java 10+

var map = new HashMap<String, List<Integer>>();
for (var entry : map.entrySet()) {
    // clean and readable
}

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JDK 10+ →

Language Beginner

Text blocks for multiline strings

Java 8

String json = "{\n" +
    "  \"name\": \"Duke\",\n" +
    "  \"age\": 30\n" +
    "}";

Java 15+

String json = """
    {
      "name": "Duke",
      "age": 30
    }""";

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JDK 15+ →

Language Beginner

Switch expressions

Java 8

String msg;
switch (day) {
    case MONDAY:
        msg = "Start";
        break;
    case FRIDAY:
        msg = "End";
        break;
    default:
        msg = "Mid";
}

Java 14+

String msg = switch (day) {
    case MONDAY  -> "Start";
    case FRIDAY  -> "End";
    default      -> "Mid";
};

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JDK 14+ →