Q:

Are there inline functions in java?

Is there a concept of inline functions in java, or its replaced something else? If there is, how is it used? I've heard that public, static and final methods are the inline functions. Can we create our own inline function?

A:

In Java, the optimizations are usually done at the JVM level.  At runtime, the JVM perform some "complicated" analysis to determine which methods to inline.  It can be aggressive in inlining, and the Hotspot JVM actually can inline non-final methods.
The java compilers almost never inline any method call (the JVM does all of that at runtime).   They do inline compile time constants (e.g. final static primitive values).  But not methods.
For more resources:

Article: The Java HotSpot Performance Engine: Method Inlining Example
Wiki: Inlining in OpenJDK, not fully populated but contains links to useful discussions.

A:

No, there is no inline function in java. Yes, you can use a public static method anywhere in the code when placed in a public class. The java compiler may do inline expansion on a static or final method, but that is not guaranteed.
Typically such code optimizations are done by the compiler in combination with the JVM/JIT/HotSpot for code segments used very often. Also other optimization concepts like register declaration of parameters are not known in java.
Optimizations cannot be forced by declaration in java, but done by compiler and JIT. In many other languages these declarations are often only compiler hints (you can declare more register parameters than the processor has, the rest is ignored).
Declaring java methods static, final or private are also hints for the compiler. You should use it, but no garantees. Java performance is dynamic, not static. First call to a system is always slow because of class loading. Next calls are faster, but depending on memory and runtime the most common calls are optimized withinthe running system, so a server may become faster during runtime!

A:

Java does not provide a way to manually suggest that a method should be inlined. As @notnoop says in the comments, the inlining is typically done by the JVM at execution time.

