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Tooling Intermediate

Class.newInstance() to constructor reflection

Replace deprecated Class.newInstance() with explicit constructor lookup and invocation.

Tooling Migration Constructors Exception Handling

Code Comparison

✕ Deprecated Class.newInstance()

Plugin plugin = pluginClass.newInstance();

✓ Constructor reflection

Plugin plugin = pluginClass
        .getDeclaredConstructor()
        .newInstance();

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Why the modern way wins

✅

Supported API

Removes use of deprecated Class.newInstance().

🎯

Explicit constructor

The requested signature is visible and can accept arguments.

🛡

Honest failures

Constructor exceptions are represented through InvocationTargetException.

Old Approach

Class.newInstance()

Modern Approach

Explicit constructor lookup

Since JDK

Difficulty

Intermediate

JDK Support

Class.newInstance() to constructor reflection

Available

Recommended since Class.newInstance() was deprecated in JDK 9 (September 2017).

How it works

Class.newInstance() is deprecated because it can bypass compile-time checking for exceptions thrown by the constructor and only supports a zero-argument constructor. Explicit Constructor lookup makes the selected signature visible and reports reflective invocation failures through the appropriate reflection exceptions. Module and access rules still apply; this pattern does not recommend bypassing encapsulation.

Class-file parsing with the standard API

Third-party bytecode parser

ClassReader reader = new ClassReader(
        Files.readAllBytes(classFile));
reader.accept(visitor, 0);

Java 24+

ClassModel model = ClassFile.of().parse(classFile);
model.methods().forEach(method ->
        System.out.println(
                method.methodName().stringValue()));

Hover to see modern ➜

JDK 24+ →

I/O Intermediate

Deprecated URL constructors to URI

Deprecated URL constructor

URL endpoint =
    new URL("https://example.com/api?q=java");

Java 20+

URI endpointUri =
    URI.create("https://example.com/api?q=java");
URL endpoint = endpointUri.toURL();

Hover to see modern ➜

JDK 20+ →

Language Intermediate

Compact canonical constructor

Java 16

public record Person(String name,
                     List<String> pets) {
    // Full canonical constructor
    public Person(String name,
                  List<String> pets) {
        Objects.requireNonNull(name);
        this.name = name;
        this.pets = List.copyOf(pets);
    }
}

Java 16+

public record Person(String name,
                     List<String> pets) {
    // Compact constructor
    public Person {
        Objects.requireNonNull(name);
        pets = List.copyOf(pets);
    }
}

Hover to see modern ➜

JDK 16+ →