Java Error Could Not Reserve Enough Space For Object Heap


The ‘Could Not Reserve Enough Space For Object Heap’ is a Java Virtual Machine (JVM) error that can bother you when you try to run a program like Minecraft Java. 

To resolve this error, you’ll want to learn background information on JVM, Java memory management, and the heap size memory variable. This guide covers all of these key points, before walking you through fixing this error, step-by-step. 

Continue reading to get this Java error fixed!

What is the ‘Could Not Reserve Enough Space for Object Heap’ Error?

The ‘Could Not Reserve Enough Space for Object Heap’ error is linked to memory mismanagement of the Java Virtual Machine. This error will prevent a Java program from running. The full error reads:

Error occurred during initialization of VM. Could not reserve enough space for object heap.

Many Minecraft players have experienced this same JVM error when trying to launch their game. If this is happening to you, it’s related to your Java installation, not the Minecraft application. This error is related to memory mismanagement and can be fixed by following the steps in solution 3. 

Java Virtual Machine (JVM)

Java Virtual Machine (JVM) is an important component of any Java program. Java source code is compiled into Byte Code (binary form) and the Java Virtual Machine acts as the Byte Code interpreter and will convert the code into the necessary machine language. 

The Java Virtual Machine is part of the Java Runtime Environment, also known as JRE. There are three key subsystems within the Java Virtual Machine:

  • Runtime Data Areas
  • Execution Engine
  • Class Loader Subsystem

The JVM handles security and memory management for Java applications. As Java programs run, objects are added to the heap. Over time the heap fills up and objects are no longer needed. Garbage collection is the main memory management process, where the garbage collector finds any unused objects when the heap is full. It deletes these unused files to free up memory. 

When you set flags like maximum heap size and heap section sizes, you can tune garbage collection to get the best Java program performance. If you fail to set the memory or choose a heap size that exceeds the system memory, the ‘Could Not Reserve Enough Space For Object Heap’ error might prevent the program from running. 

Java Memory Management 

To manage memory for Java programs, there are some important basics you need to know. The Java Virtual Machine has three main memory components:

  • Heap Memory – the primary run time area for java class instances and arrays. It can increase or decrease dynamically during runtime. Any objects within heap memory can be shared between the threads while the application runs. 
  • Non-Heap Memory – created when the virtual machine starts, stores the runtime constant pool, method and constructors coding, and interned strings. Non-heap memory has a maximum size of 64 MB.
  • Other – the ‘other’ memory space holds important JVM components such as internal JVM structures and the loaded profiler agent

What is Heap Size?

Java Virtual Machine heap memory can be adjusted by changing the heap size. By default, the heap size is 1280 MB. Let’s look at some guidelines for Heap sizing, to help you select a heap size across various platforms:

  • Redhat Linux 32-bit – 2 GB
  • RedHat Linux 64-bit – 3 GB
  • Windows 98/2000/NT/Me/XP – 2 GB
  • Solaris 32-bit – 4 GB
  • Solaris 64-bit – Terabytes

You can set the heap size, using the -Xms option.

What is Max Heap Size?

You may be interested to know the maximum heap size of your system so that you know how high you can set it. A large memory heap can allow more objects to be created while taking longer to fill and allows longer periods between garbage collection events. While a small memory heap may cause out-of-memory errors, hold fewer objects, and fill more quickly. 

You want to select an optimized value for your computer so that performance is not negatively impacted by frequent garbage collection events to free up RAM. The general rule-of-thumb for max heap size is 1/4th of your system’s physical memory or 1GB. Whichever is smaller will be the default max heap value. 

You can override the max heap size, using -Xmx.

What Causes the ‘Could Not Reserve Enough Space for Object Heap’ Error?

The ‘Could Not Reserve Enough Space for Object Heap’ error has three primary causes. Resolving these causes will fix the Java error and allow your Java program to run correctly. This error ultimately comes down to memory mismanagement. If JRE has memory settings improperly assigned (or not at all), then your program can’t run properly and the error will be thrown.

1. Not Specifying Memory for Java

If the memory hasn’t been specified  for that program, then the following error message will be returned:

Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

2. Memory Greater Than Heap Size

If the memory has been specified for 32-bit JVM, but it exceeds the JVM heap size, this error might appear. 

3. Heap Memory Greater than Physical Memory

If heap memory has been specified to exceed the physical memory the ‘Could Not Reserve Enough Space for Object Heap’ will appear. If you’re experiencing issues with your Minecraft game, this is the cause. 

How to Fix the ‘Could Not Reserve Enough Space for Object Heap’ Error

You can address the three memory-related causes for this Java error, by following the step-by-step solutions below.

1. Specify Memory 

Most of the time, memory specification issues are linked to 32-bit JVM. So, the error happens when you attempt to use a 32-bit Java Virtual Machine on systems with large physical memory. 

Or, perhaps, the native memory may be low. Normally, if the maximum heap size is not specified then, JVM automatically attempts to reserve a large heap, usually half of the physical memory. But with modern hardware, the physical memory may be much larger. 

When JVM calculates the heap size, this can be a very large value at 50% of the physical memory. The maximum heap size for 32-bit JVM is 2 GB. 

To get around this problem, you can replace the 32-bit Java Virtual Machine with a 64-bit JVM for use in 64-bit computer systems. Alternatively, you can manually specify the maximum heap size (instead of allowing it to automatically set) using the following command on the command-line interface:

java -Xmx256M program_name

2. Adjust Memory Size Within JVM Limits

If the memory size has been set to exceed the maximum heap size of a 32-bit JVM then the ‘Could Not Reserve Enough Space for Object Heap’ error might appear. For example, if the system has 2 GB of memory, but it is set to 2006M using the following command, the error will trigger:

java -Xms2206M -Xmx2006M program_name 

To fix this problem, you can use 64-bit JVM or set the memory size appropriately: 

java -Xms1336M -Xmx1336M program_name

3. Adjust Heap Size

If heap size has been set to exceed the physical memory limits of an application, this error will appear. Of course, you can set a smaller heap memory that falls within the physical memory limits, just like you did in solution 2:

java -Xms1336M -Xmx1336M program_name

You can also specify the memory size from the _JAVA_OPTIONS variable in path. JVM will use the memory size set in this variable. For Windows systems you can change this variable by following these steps:

To create a new System Variable to increase the size of the global maximum heap memory size for Java, follow the steps below:

  1. Press Windows key + R and the Run dialog box will open. Enter sysdm.cpl into the search box and press Enter. 
Could Not Reserve Enough Space for Object Heap - start fix
  1. The System Properties window will open. Select the Advanced tab and then Environment Variables.
environment variables - Could Not Reserve Enough Space for Object Heap error fix
  1. From the Environment Variables window, under System Variables, select New
system variables option
  1. A new window will open. For Variable name, enter _JAVA_OPTIONS and set Variable value to –Xmx256M. The Xmx512M setting will allocate 256 Megabytes of RAM to global maximum heap memory. Click OK.
new systems variable - java options
  1. Close all windows and restart your system. Then attempt to open the application that was displaying the ‘Could not create the Java Virtual Machine’ error, to see if the problem is resolved.

‘Could Not Reserve Enough Space for Object Heap’ Error Resolved

The ‘Could Not Reserve Enough Space for Object Heap’ revolves around memory mismanagement, especially for 32-bit Java Virtual Machines. In general, 32-bit hardware architecture and 32-bit JVM should be avoided. 64-bit systems are available and should be used in almost all cases, to prevent this kind of issue. 

It’s important to learn the fundamentals of Java management and heap size, before changing any variables. Once you know the basics, you can adjust heap size to improve performance and limit garbage collection events. You can resolve this error by specifying the memory and adjusting heap size settings to suit the JVM version and physical memory. 

Follow the guidelines outlined in this article to know what is the maximum heap size for your system. Now that you’ve resolved the memory issues, your Java application should open without returning any errors.

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