面试题与答案

The another long-term support(LTS) release for the Java SE platform is Java 17 LTS. The previous LTS version was Java 11. Under the Oracle No-Fee Terms and Conditions License, JDK 17 binaries are free to use in production and redistribute at no cost with the help of OpenJDK. LTS stands for long-term support. It is available from September, 2021. For OracleJDK it is mandatory to purchase the license but it is absolutely free to use OpenJDK.

To check the detail difference, please check here: OracleJDK vs OpenJDK 💯💯

The new features added in Java 17 are as follows:

• Restore or Rebuild the "Always-Strict Floating-Point" Semantics
• Enhanced faster the "pseudo-Random" Number Generators
• New macOS rendering pipelines
• macOS/AArch64 Port
• Dismiss the Applet API for Removal
• JDK Internals Encapsulate strongly
• Switch Pattern Matching (Preview)
• Activation of the Removal RMI
• Generate sealed Classes
• Removal of the Experimental AOT and JIT Compiler
• Remove the Security Manager.
• Foreign Functions and Memory API (Incubator)
• Vector API (Second Incubator)
• Deserialization Filters Based on Context (content-specific)

This JEP makes floating-point operations uniformly stringent and is primarily intended for scientific applications. Both default floating-point operations, strict or strictfp, provide the same outcomes for calculations using floating-point on every platform.

Most browsers will no longer support the applet API because it has been deprecated since JDK9.

Java 17 version marked it for removal even though it has been marked as deprecated since version 9.

RMI's use in the web technology of the previous ten years has rendered the RMI activation mechanism outdated.

Marked for removal in version 15, this JEP removed the RMI activation API from the platform in version 17.

Introduced into JDK 9 and JDK 10, respectively, as experimental features, the Ahead-Of-Time (AOT) compilation and Just-In-Time (JIT) compiler from GraalVM were features with a high cost of maintenance.

Taken out the trial versions of the java-based AOT (ahead-of-time) and JIT (just-in-time) compilers from Java 17.

It makes switch statements and expressions more flexible and expressive by letting patterns appear in case labels. It also makes it possible to relax the switch's null-hostility when needed.

There are two main patterns, which are as follows:

• Guarded pattern: Uses pattern && boolean expression to refine further.
• Pattern between parentheses

static record Human (String name, int age, String profession) {}

public String checkValue(Object obj) {
    return switch (obj) {
        case Human h -> "Name: %s, age: %s and profession: %s".formatted(h.name(), h.age(), h.profession());
        case Circle c -> "This is a circle";
        case Shape s -> "It is just a shape";
        case null -> "It is null";
        default -> "It is an empty";
    };
}

public String checkShape(Shape shape) {
    return switch (shape) {
        case Triangle t && (t.getNumberOfSides() != 3) -> "This is a weird triangle";
        case Circle c && (c.getNumberOfSides() != 0) -> "This is a weird circle";
        default -> "Just a normal shape";
    };
}

You can download Java 17 from the Oracle website: https://www.oracle.com/java/technologies/downloads/#java17

It offers a new interface type and solutions for pseudo-random number generators to make using multiple PRNG (Pseudo-Random Number Generators) algorithms simpler and properly support stream-based operations.

Example: RandomGeneratorFactory

public IntStream getPseudoVals(String algorithm, int streamSize) {    
    // returns an IntStream with size @streamSize of random numbers generated using the below @algorithm    
    // where the lower bound is 0 and the upper is 100 (exclusive)    
    return RandomGeneratorFactory.of(algorithm).create().ints(streamSize, 0,100);
}

The Vector API works with Single Instruction, Multiple Data / SIMD operations, which include multiple sets of instructions being processed concurrently. It uses specialized CPU hardware that provides vector instruction and enables the operation of these instructions as pipelines.

The new API will consequently give programmers the ability to write more effective code. It makes better use of the capabilities of the underlying hardware.

Few of the operations can be enhanced with Vector API: scientific algebra linear applications, image processing, character processing, and any heavy arithmetic application or any application that needs to apply an operation for multiple independent operands.

Firstly introduced by the JDK 9 version, makes it possible for us to verify receiving serialized data from untrusted sources, which is a frequent source of security problems.

In Java 17, applications can configure dynamically chosen and context-specific deserialization filters. Each deserialization operation will invoke such filters.

Since Java 17 new JEP 403 eliminates the flag -illegal-access, it signals a step toward strongly enclosing JDK internals.

If the flag is present and the platform will disregard the flag, then the console will send out a message to stop using the given flag.

This feature will prevent JDK users from accessing internal APIs, except for critical ones like sun.misc.Unsafe.

Java programmers can retrieve code from outside the JVM. Thanks to the Foreign Function and Memory API, it controls memory outside of the heap.

The intention is to replace the JNI API and enhance its performance and security over the previous version.

Adds sealed classes and interfaces to the Java language to make it better. Sealed classes and interfaces limit other classes, and interfaces can extend and implement them, respectively.

Showing some other progress to pattern matching along with the JEP 406 will make it possible to check the type, cast, and act code pattern more sophisticatedly and cleanly.

public abstract sealed class Subjects  

permits English, Maths, Science {...}  

This JEP makes a Java 2D internal processing pipeline for macOS since Apple removed the OpenGL API in macOS 10.14. The Swing GUI used the OpenGL API.

Apart from the underlying engine, there were no modifications to the current APIs because the implementation uses the Apple Metal API.

Apple announced a long-term strategy to switch its computer line from X64 to AArch64. With the help of this JEP, the JDK may now run on macOS platforms with AArch64.

Reject the Security Manager so it can be taken out in a later update. For several years, it was never the main method of protecting client-side code.

The security manager aimed to secure client-side Java code is yet another feature marked for removal due to not being relevant anymore.

The example is as follows:

public void newVectorComputation(float[] a, float[] b, float[] c) {
    for (var i = 0; i < a.length; i += SPECIES.length()) {
        var m = SPECIES.indexInRange(i, a.length);
        var va = FloatVector.fromArray(SPECIES, a, i, m);
        var vb = FloatVector.fromArray(SPECIES, b, i, m);
        var vc = va.mul(vb);
        vc.intoArray(c, i, m);
    }
}

public void commonVectorComputation(float[] a, float[] b, float[] c) {
    for (var i = 0; i < a.length; i ++) {
        c[i] = a[i] * b[i];
    }
}

The next LTS (Long Time Support) version is Java 21 and is released in September 2023.