Learn how to store data in objects

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Last updated: January 2020

Although the snooze button is probably the most commonly used button on an alarm clock, even a simple AlarmClock class needs a few more features. For instance, you might want to control how long the alarm clock will stay in snooze mode. In order to add such a feature, you need to understand how Java controls data.

Developers use variables in Java to hold data, with all variables having a data type and a name. The data type determines the values that a variable can hold. In this tutorial, you’ll learn how integral types hold whole numbers, floating point types hold real numbers, and string types hold character strings.

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Eclipse readies next enterprise Java for mid-2020

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The Eclipse Foundation plans to release Jakarta EE 9, a version of enterprise Java with the new jakarta.* namespace, in mid-2020. Jakarta EE 9 will not have major new functionality.

A key goal of Jakarta EE 9 is to lower the barrier to entry to new vendors and implementations. Primarily seen as a tooling release, Jakarta EE 9 is intended to:

  • Serve as a platform for developers to use as a stable target for testing migration to the new namespace. Eclipse has been unable to gain permission from Oracle to evolve specifications under the previous javax namespace.
  • Make the release available quickly as a platform for innovation.

Jakarta EE 9 represents a “major inflection point” in the platform, Eclipse Executive Director Mike Milinkovich said. Key elements of the release plan include moving all specification APIs to the jakarta namespace and eliminating unwanted and deprecated specifications.

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What is the JVM? Introducing the Java Virtual Machine

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The Java Virtual Machine is a program whose purpose is to execute other programs. It’s a simple idea that also stands as one of our greatest examples of coding kung fu. The JVM upset the status quo for its time, and continues to support programming innovation today.

What the JVM is used for

The JVM has two primary functions: to allow Java programs to run on any device or operating system (known as the “Write once, run anywhere” principle), and to manage and optimize program memory. When Java was released in 1995, all computer programs were written to a specific operating system, and program memory was managed by the software developer. So the JVM was a revelation.

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What is the JRE? Introduction to the Java Runtime Environment

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Together, the Java Development Kit (JDK), the Java Virtual Machine (JVM), and the Java Runtime Environment (JRE) form a powerful trifecta of Java platform components for developing and running Java applications. I’ve previously introduced the JDK and JVM. In this quick tutorial, you’ll learn about the JRE, which is the runtime environment for Java.

Practically speaking, a runtime environment is a piece of software that is designed to run other software. As the runtime environment for Java, the JRE contains the Java class libraries, the Java class loader, and the Java Virtual Machine. In this system:

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What is the JDK? Introduction to the Java Development Kit

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The Java Development Kit (JDK) is one of three core technology packages used in Java programming, along with the JVM (Java Virtual Machine) and the JRE (Java Runtime Environment). It’s important to differentiate between these three technologies, as well as understanding how they’re connected:

  • The JVM is the Java platform component that executes programs.
  • The JRE is the on-disk part of Java that creates the JVM.
  • The JDK allows developers to create Java programs that can be executed and run by the JVM and JRE.

Developers new to Java often confuse the Java Development Kit and the Java Runtime Environment. The distinction is that the JDK is a package of tools for developing Java-based software, whereas the JRE is a package of tools for running Java code.

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