What is System.gc() and Runtime.gc()?
A typical Garbage Collection (GC) algorithm in Java identifies garbage by traversing all non-garbage objects in the heap, and inferring that any object not visited must be garbage. Calling one of the gc() methods does not force garbage collection to happen, either; it only suggests to the JVM that now might be a good time for some garbage collection.
System.gc() is used to invoke the garbage collector and on invocation garbage collector will run to reclaim the unused memory space. It will attempt to free the memory that are occupied by the discarded objects. The System.gc() is a static method so it's a little bit more convenient to use. Calling it can add unnecessary performance issues to your application, and it is not guaranteed to actually perform a collection. It is actually possible to disable explicit System.gc() via the java argument -XX:+DisableExplicitGC. The Java Language Specification does not guarantee that the JVM will start a GC when you call System.gc().
Java Runtime class is used to interact with java runtime environment. The java.lang.Runtime.gc() method runs the garbage collector. Calling this method suggests that the JVM (Java virtual machine) expend effort toward recycling unused objects in order to make the memory they currently occupy available for quick reuse. When control returns from the method call, the virtual machine has made its best effort to recycle all discarded objects.
system.gc() VS runtime.gc()
Both are same. There is no difference between System.gc() and Runtime.gc() . System.gc()internally calls Runtime.gc(). The only difference is System.gc() is a class method whereas Runtime.gc() is an instance method. So, System.gc() is more convenient. Also, Runtime.gc() is a native method whereas System.gc() is non - native method which in turn calls the Runtime.gc()
- Java Interview Questions-Core Faq - 1
- Java Interview Questions-Core Faq - 2
- Important features of Java
- What is the difference between JDK and JRE?
- What gives Java its 'write once and run anywhere' nature?
- What is JVM and is it platform independent?
- What is Just-In-Time (JIT) compiler?
- What is the garbage collector in Java?
- What is NullPointerException in Java
- Difference between Stack and Heap memory in Java
- How to set the maximum memory usage for JVM?
- What is numeric promotion?
- Why do we need Generic Types in Java?
- What does it mean to be static in Java?
- What are final variables in Java?
- How Do Annotations Work in Java?
- How do I use the ternary operator in Java?
- What is instanceof keyword in Java?
- How ClassLoader Works in Java?
- What are fail-safe and fail-fast Iterators in Java
- What are method references?
- "Cannot Find Symbol" compile error
- How to convert TimeStamp to Date in Java?
- Does garbage collection guarantee that a program will not run out of memory?
- How setting an Object to null help Garbage Collection?
- How do objects become eligible for garbage collection?
- How to calculate date difference in Java
- Difference between Path and Classpath
- Is Java "pass-by-reference" or "pass-by-value"?
- Difference between static and nonstatic methods java
- Why Java does not support pointers?
- What is package in Java?
- What are wrapper classes?
- What is singleton class in Java?
- Difference between Local Variable, Instance Variable and a Class Variable in Java?
- Can a top level class be private or protected in java
- Are Polymorphism , Overloading and Overriding similar concepts?
- How to Use Locks in Java
- Why Multiple Inheritance is Not Supported in Java
- Why Java is not a pure Object Oriented language?
- Why can't a Java class be declared as static?
- Difference between Abstract class and Interface in Java
- Why do I need to override the equals and hashCode methods in Java?
- Why does Java not support operator overloading?
- What’s meant by anonymous class in Java?
- Static Vs Dynamic class loading in Java
- Why am I getting a NoClassDefFoundError in Java?
- How to generate random integers within a specific range in Java
- What's the meaning of System.out.println in Java?
- What is the purpose of Runtime and System class?
- What is finally block in Java?
- What is difference between final, finally and finalize?
- What is try-with-resources in java?
- What is a stacktrace?