Java

Java is a statically typed, object-oriented programming language released by Sun Microsystems in 1995. Source code is compiled to bytecode, which the Java Virtual Machine (JVM) executes, so the same compiled program can run on any system with a compatible JVM.

Why it matters

Java underpins a large share of enterprise back ends, banking systems, big data tools and Android apps (alongside Kotlin). The JVM provides automatic memory management, mature tooling and strong backward compatibility, which is why decades-old Java code still runs. Frameworks such as Spring dominate server development. The language is more verbose than many newer ones, and JVM start-up and memory use can matter for small services.

Example

public class Hello {
    public static void main(String[] args) {
        String name = "SiteDownCheck";
        System.out.println("Hello, " + name);
    }
}

The javac compiler turns this into Hello.class, and java Hello runs it on the JVM.

Common mistakes

• Comparing strings with == instead of .equals(), which compares references.
• Forgetting that null can be assigned to any object variable, leading to NullPointerException.
• Confusing Java with JavaScript; they are unrelated languages.

Related

• Object-oriented programming
• Garbage collection
• Kotlin
• Null

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