Java.Collections.WeakHashMap uses WeakReferences. Why not create a SoftHashMap on SoftReferences?

✅ Difference Between WeakReference and SoftReference

Feature	WeakReference	SoftReference
GC behavior	Collected as soon as no strong refs	Collected only when memory is low
Lifespan	Short	Longer (survives longer in memory)
Use case	Automatic cleanup	Memory-sensitive cache

So in theory:

✅ WeakHashMap → removes entries aggressively
✅ SoftHashMap → removes entries only if memory is tight → perfect for caching

🧪 So does SoftHashMap exist?

❌ No, Java doesn’t provide one by default in the standard library.
But…

🧰 You can totally implement your own!

Using SoftReference keys or values.

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✅ Common patterns:

1. SoftReference for values (most common)
   • Key is strong, value is SoftReference.
   • Used in things like image caches (e.g., Android).
2. SoftReference for keys (less common, trickier)
   • Need to track when keys are collected, like WeakHashMap does.

🛠️ DIY SoftValueMap (simplified example)

import java.lang.ref.SoftReference;
import java.util.*;

public class SoftValueMap<K, V> {
    private final Map<K, SoftReference<V>> map = new HashMap<>();

    public void put(K key, V value) {
        map.put(key, new SoftReference<>(value));
    }

    public V get(K key) {
        SoftReference<V> ref = map.get(key);
        return (ref != null) ? ref.get() : null;
    }
}

✅ This acts like a map that drops values when memory is low.

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🤖 Real-Life Example: Guava Cache

Google’s Guava library has:

CacheBuilder.newBuilder()
    .softValues()
    .build();

That’s a production-ready SoftHashMap-style cache, handling thread safety, cleanup, and expiration.

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🧠 TL;DR:

Java doesn’t have a built-in SoftHashMap, but the idea is legit and used in real-world caching.

✅ Use SoftReference if you want memory-aware caching that holds data as long as memory is available.