Wrapper Class Caching

May 31, 2020 1-minute read

java

java • heap • stack

Wrapper Class Caching:

Added in JAVA 5. It is used to improve the performance and save memory. It only works on autoboxing.

Byte : private static ByteCache inner class : Range -127 to +127
Short : private static ShortCache inner class : Range -127 to +127
Long : private static LongCache inner class : Range -127 to +127
Integer : private static IntegerCache inner class : Range -127 to +127
Character : private static CharacterCache inner class : Range 0 to +127

We can be modified this range only for Integer by using a VM argument -XX:AutoBoxCacheMax=size


    Integer x = 10; //autoboxing
    Integer y = Integer.valueOf(10); // Compiler converts 10 to Integer.valueOf(10) when doing autoboxing.
    Integer z = new Integer(100);
    
    System.out.println(x == y); // true
    System.out.println(x == z); // false
    System.out.println(y == z); // false
    
    Integer x1 = 128; //autoboxing
    Integer x2 = 128; //autoboxing
    System.out.println(x1 == x2); // false   
    
    // Integer's valueOf API
    public static Integer valueOf(int i) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }