Java memory management: tips and tricks for efficient memory management

Java is a popular programming language that is used to develop complex applications. One of the common problems with Java programs is high memory consumption, which can cause performance problems and even application crashes in extreme cases. Whether you’re a Java developer or a senior Java developer, you know that it’s important to use memory saving techniques to optimize your Java code and reduce memory consumption wherever possible. In this article, we will go through some of the best practices and memory saving tips in Java.

Use efficient data structures

The choice of an appropriate data structure has a significant impact on the efficiency and speed of Java programming. For example, preferring LinkedList over ArrayList can be advantageous if you frequently add or remove items from a list because it has constant time complexity for these operations as opposed to the linear time complexity of ArrayList.
HashMap, TreeSet, and PriorityQueue are a few other effective data structures to use in your programs depending on the situation. By taking advantage of these data structures, you can improve the overall performance of your Java code.

Avoid writing long methods

Methods should not be too long and should be aimed at performing a single function. This is better not only for maintenance, but also for performance, since the method is loaded into the stack memory during class loading and method calling. If methods are large and contain too many statements, they consume both memory and CPU cycles more heavily during execution. Therefore, try to break long methods into smaller, logical units.

Avoid creating unnecessary objects

Constantly creating objects in Java can consume a lot of memory and slow down your code because allocated and unused memory needs to be recycled. Whenever possible, try to reuse existing things rather than create new ones. One technique to achieve this is pooling, which is the maintenance of a set of reusable objects that can be borrowed and returned as needed.

As an alternative to repeatedly creating new objects, you can use, for example, the Flyweight design pattern.

Flyweight design pattern

Flyweight is a design pattern that is used to share objects and reduce memory consumption. In this example, you can reuse the same key object instead of creating a new one when retrieving a value from the list. This way you can save memory by reducing the number of objects created.

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String in Java is an immutable class and an object created with String cannot be reused. Consider the following line of code:

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In this example, you need to concatenate several strings into one. The problem is that Java first creates an object of type String for each string and then concatenates them. To avoid this, you can use StringBuilder to concatenate text strings.

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Use mainly primitive data types

The use of primitive types is preferred over objects because primitive type data is stored in stack memory and objects are stored in heap memory. And just accessing data in the stack memory is much faster than in the heap.

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Avoid unnecessary autoboxing

Autoboxing is the automatic conversion of primitive types to their corresponding wrapper objects.Avoid unnecessary autoboxing However, this can cause unnecessary object creation and excess memory costs. Instead, you can use the valueOf() method of the Integer object to avoid autoboxing and reuse existing objects.

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Avoid using the BigDecimal class

We know that the BigDecimal class provides high precision for calculations with decimal numbers. However, excessive use of these objects drastically limits performance, especially when used in cycles. BigDecimal uses a lot of memory to perform calculations compared to long and double types. If precision is not the main criterion, or if you are sure that the range of the calculated value will not exceed long or double, you can avoid using BigDecimal and instead use long or double with proper pretyping.

Use lazy initialization

Instead of initializing the list of objects when the class is loaded, you can use the so-called delayed object initialization. This means that object initialization (and therefore memory allocation) is delayed until it is needed. This way we can save memory by avoiding the creation of unnecessary objects.

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Use fields instead of collections

Instead of using an ArrayList collection, you can use a simple array when you know the number of elements in advance. This way you can save memory by avoiding the cost of dynamic zoom in/out and other methods needed to initialize the collection.

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Reuse created objects repeatedly

Always try to reuse created objects and don’t unnecessarily create new ones unless necessary.

In this example, instead of creating a new ArrayList for each iteration of the loop, you can reuse the same object by cleaning it up after each use. Týmto spôsobom môžete ušetriť pamäť znížením počtu vytvorených objektov.

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Use the intern() method

The intern() method is a method of the String class that returns a canonical representation of the string. Using intern(), you can ensure that only one instance of a string is created, even if the same string is created multiple times. This way you can save memory by reducing the number of strings created.

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Using these memory-saving techniques, you can optimize your Java code to be more efficient and consume less memory.

However, it is important to remember that memory optimization should not come at the expense of readability or code sustainability. Developers should carefully consider the trade-offs between memory consumption and code quality to ensure that their applications are performant and reliable.

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About the author

Jozef Wagner

Java Developer Senior

Viac ako 10 rokov programujem v Jave, momentálne pracujem v msg life Slovakia ako Java programátor senior a pomáham zákazníkom implementovať ich požiadavky do poistného softvéru Life Factory. Vo voľnom čase si rád oddýchnem v lese, prípadne si zahrám nejakú dobrú počítačovú hru.

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