What is the Difference Between System gc and Runtime gc in Java? with Proper Definition and Brief Explanation

The main difference between System gc and Runtime gc in Java is that System gc is a class method, while Runtime gc is an instance method.

Java is a high-level, general-purpose programming language. It is robust and secure, provides platform independence, and supports multi-threading. In addition, it allows object-oriented programming. Therefore, it is easier to model real-world scenarios to create applications using Java. Another major advantage of Java is that it provides a garbage collector, which destroys unused objects automatically to provide better memory management. Running the garbage collector is an automatic process, but it is also possible to request the JVM to run the garbage collector. System gc and Runtime gc are two such methods to request JVM to run garbage collector.

Key areas covered

1. What is System gc in Java
     – Definition, Functionality
2. What is Runtime gc in Java
 – Definition, Functionality
3. What is the relationship between System gc and Runtime gc?
     – Association scheme
4. What is the difference between System gc and Runtime gc?
     – Comparison of key differences

Key terms

Gc system, gc runtime

What is System gc?

In the system class, there is a method called gc (). The garbage collector runs. This method invokes the finalize () method to destroy the objects that are not used. In Java, objects are created on the heap.

Generally, the JVM calls the garbage collector implicitly. However, it won’t call the garbage collector unnecessarily. Suppose there are only a few objects in the heap. So JVM won’t invoke garbage collector. It will only invoke the garbage collector when the heap memory is less.  

                                              Figure 1: JVM architecture

For example, suppose a new object needs to be created and the heap is low on memory. First, the garbage collector will look for an object without a reference. Then it will invoke the completion method. You will then free up the allocated resources of that object and destroy the object. Finally, the JVM will allocate that memory to the newly created object. This whole process takes more time. Instead, the programmer can call the System.gc () method. It is a request to the JVM to run the garbage collector continuously in the background.

What is Runtime gc?

Runtime gc task is the same as System gc. It is a method that tells the JVM to run the garbage collector continuously. Unlike Runtime gc, which is a class method, Runtime gc is an instance method. A major problem in System gc and Runtime gc is that they can cause performance problems.

Relationship between System gc and Runtime gc

  • gc () internally calls Runtime.gc ().

Difference between System gc and Runtime gc

Definition

System gc is a class method that suggests that the Java Virtual Machine (JVM) run the garbage collector to get memory from unused objects to create memory for current objects. Runtime gc is an instance method that suggests that the Java Virtual Machine (JVM) run the garbage collector to get memory from unused objects to create memory for current objects. 

Base

Therefore, the main difference between System gc and Runtime gc is that the system gc is a class method, while the runtime gc is an instance method.

Type

Another difference between System gc and Runtime gc is that system gc is a non-native method, while runtime gc is a native method.

Statement

The declaration for the java.lang.System.gc () method is public static void gc ()

The declaration of the java.lang.Runtime.gc () method is public void gc ()

conclusion

The garbage collector frees heap memory by destroying unreachable objects. System gc and Runtime gc are two methods to request the JVM to run the garbage collector. The basic difference between System gc and Runtime gc in Java is that System gc is a class method, while Runtime gc is an instance method. Typically, System gc is more convenient than Runtime gc.

Reference:

1. What is the use of System.gc ()? | Top Java Interview Questions, Naresh i Technologies, March 1, 2017, Available here.
2. “Java.lang.System.gc () Example of the method.” Www.tutorialspoint.com, Available here.
3. “Java.lang.Runtime.gc () Example of the method.” Www.tutorialspoint.com, Available here.
4. “Garbage collection in Java”. GeeksforGeeks, September 7, 2018, Available here.

Courtesy Image:

1. “Java Virtual Machine Architecture” By Dcoetzee (File: Computer-blue.svg by OpenClipart, File: Phone-blackberry-bold.svg by User: Techtoucian) – Own work (CC0) via Commons Wikimedia

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