Load Factors for ArrayList and HashMap

Introduction

The load factor is a crucial concept in data structures, particularly for collections like ArrayList and HashMap in Java. It defines how full a data structure can get before it needs to be resized or rehashed.

Load Factor in ArrayList

An ArrayList is a resizable array implementation of the List interface. It dynamically increases its size as elements are added.

Key Points

• The default initial capacity of an ArrayList is 10.
• The load factor is implicitly managed; when the number of elements exceeds the current capacity, a new array (typically double the size) is created and the existing elements are copied over.

Example

        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        // On adding more elements than the current capacity, the ArrayList resizes itself.

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Load Factor in HashMap

A HashMap is a data structure that stores key-value pairs and uses hashing to provide efficient access to elements.

Key Points

• The load factor is a measure that determines when to increase the capacity of the map. The default load factor is 0.75, which offers a balance between time and space costs.
• When the number of entries exceeds the product of the load factor and the current capacity, the map is resized (doubled) and the existing entries are rehashed.

Example

        HashMap<String, String> map = new HashMap<>();
        map.put("Key1", "Value1");
        map.put("Key2", "Value2");
        // If entries exceed the load factor threshold, the HashMap resizes itself.

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Conclusion

Understanding load factors for ArrayList and HashMap helps developers choose the right data structure for their needs. For ArrayList, resizing happens automatically, whereas for HashMap, careful consideration of load factors can enhance performance by minimizing collisions and optimizing memory usage.

原文链接：Explain Load Factors for ArrayList and HashMap in Java