Identity Vs Equality Comparison of Integers in Java

Identity comparison:

        Identity comparison compares the address of values or object references.

Equality comparison:

• Equality comparison compares the values.
• == Operator performs identity comparison for object types(wrapper classes) in java.
• == Operator performs equality comparison for basic Primitive types in java.
• equals method performs equality comparison for object types in java.

Example:

    int i = 100;
    int j = 100;

    System.out.println(i == j) //will return true as output 

Here value 100 is stored in memory at particular location. variable i and j points the same location 100 is present.

Integer i1 = 127; 
Integer i2 = 127;

Here primitive int 127 is auto boxed to integer wrapper class and variable i1 is pointing the location in Integer Cache and another 127 is auto boxed to integer wrapper class and i2 pointing the same location of 127 in Integer Cache.

What is Integer Cache?

       

Integer cache was introduced in java 5 which was introduced to improve the memory performance for Integer type objects. Integer objects are cached internally and reused via same referenced objects.

        1. java.lang.Integer.IntegerCache contains low value -128 and high value 127

There are totally 256 values are cached in Integer cache.

        2. The integer caching works only on auto boxing. Integer Objects will not cached when they are built using constructor.

System.out.println(i1 == i2) //will return true as output 

Here 127 is the last value in IntegerCache so i1 and i2 pointing the location in Integer cache memory which is also in same location

System.out.println(i1.equals(i2)) //will return true as output 

equals method always unbox the Integer wrapper class into primitive type and compare the values and uses intValue() method to unbox to primitive int.

equals method in Integer Class:

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public boolean equals(Object obj) { if (obj instanceof Integer) { return value == ((Integer)obj).intValue(); } return false; }

Here equals method convert the wrapper class Integer to primitive int and perform == operation, see the equals method definition in Integer class.

Integer i1=new Integer(127); 
Integer i2=new Integer(127); 

Here primitive int 127 is  boxed to integer wrapper class in 2 new location (i.e) i1 and i2 are pointing to 2 different locations.

System.out.println(i1 == i2) //will return false as output 

==  always perform identity check (location check)

Here, though 127 is present as a value in IntegerCache, because of new Integer() constructor i1 and i2 are created in two new different location but not in Integer Cache because of different location reference i1 == i2 returns false.

System.out.println( i1.equals(i2)); //will return true as output 

equals method always unbox the wrapper class into primitive type and compare the values and uses intValue() method to unbox to primitive int

Here equals method unbox the wrapper class Integer to primitive int and perform == operation, see the equals definition in Integer class

Integer i1=128; 
Integer i2=128; 

Here 128 is not in Integer Cache, so  new location in allocated for 128 refer valueOf() method in Integer Class.

valueOf method in Integer Class:

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public static Integer valueOf(int i) { if(i >= -128 && i <= IntegerCache.high) return IntegerCache.cache[i + 128]; else return new Integer(i); }

valueOf method checks whether the passing int is in between the low and high cache value if not, then assign new location by calling new Integer constructor.

System.out.println (i1 == i2); //will return false as output

Here the value 128 is not present in IntegerCache so it  gets wrapped like new Integer(128)  i1 and i2 are created in two different location but not in Integer Cache

System.out.println (i1.equals(i2)); //will return true as output 

equals always unbox the wrapper class into primitive type and compare the values and uses intValue() method to unbox to primitive int.

Here equals method unbox the wrapper class Integer to primitive int and perform == operation, see the equals definition in Integer class.

Comparing Integer with int:

Integer i1=128; //wrapper class
int i3=128;  //primitive int

Here 128 is not in Integer Cache , new location in allocated for 128.

System.out.println(i1 == i3); //will return true as output 

Here i1 is Integer and i3 is primitive int, so Integer is unboxed to primitive int automatically and perform identity check of (int 128 == int 128 ).

System.out.println(i1.equals(i3)); //will return true as output.

equals method always unbox the wrapper class into primitive type and compare the values and uses intValue() method to unbox to primitive int.

Here equals method unbox the wrapper class Integer to primitive int and perform == operation, see the equals definition in Integer class.

Comparison of integer values not present in Integer cache can be achieved by == operator:

Integer  i1 = new Integer(128); //new memory
Integer  i2 = new Integer(128); //new memory
System.out.println (i1 == i2.intValue ()); //will return true as output.

Here equality comparison is achieved programmatically by unboxing the Integer to primitive int.

I hope now you got some idea in this topic ☺☺☺ Keep Exploring...