What is Just-In-Time compiler in Java?

The Just-In-Time (JIT) compiler is introduced after initial version of Java. In the initial version there was an interpreter due to which the performance of java programs was less (executed slowly). So, they replaced the interpreter with the JIT compiler.

JIT compiler uses hotspot technology. When JVM is executing a java program, the JIT compiler compiles only the necessary set of instructions and those instructions are loaded into the memory and are executed. Due to this java programs are executed at greater speed.