How can I properly compare two Integers in Java?

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I know that if you compare a boxed primitive Integer with a constant such as:

Integer a = 4;
if (a < 5)

a will automatically be unboxed and the comparison will work.

However, what happens when you are comparing two boxed Integers and want to compare either equality or less than/greater than?

Integer a = 4;
Integer b = 5;

if (a == b)

Will the above code result in checking to see if they are the same object, or will it auto-unbox in that case?

What about:

Integer a = 4;
Integer b = 5;

if (a < b)

?

autoboxing integer java
10 Answers

We should always go for the equals() method for comparison of two integers. It's the recommended practice.

If we compare two integers using == that would work for certain range of integer values (Integer from -128 to 127) due to the JVM's internal optimisation.

Please see examples:

Case 1:

Integer a = 100;
Integer b = 100;

if (a == b) {
  System.out.println("a and b are equal");
} else {
  System.out.println("a and b are not equal");
}

In above case JVM uses value of a and b from cached pool and return the same object instance(therefore memory address) of integer object and we get both are equal.Its an optimisation JVM does for certain range values.

Case 2: In this case, a and b are not equal because it does not come with the range from -128 to 127.

Integer a = 220;
Integer b = 220;
   
if (a == b) {
  System.out.println("a and b are equal");
} else {
  System.out.println("a and b are not equal");
}

Proper way:

Integer a = 200;             
Integer b = 200;  
System.out.println("a == b? " + a.equals(b)); // true
user_53266340

In my case I had to compare two Integers for equality where both of them could be null. I searched similar topics, but I didn't find anything elegant for this. I came up with simple utility function:

public static boolean integersEqual(Integer i1, Integer i2) {
    if (i1 == null && i2 == null) {
        return true;
    }
    if (i1 == null && i2 != null) {
        return false;
    }
    if (i1 != null && i2 == null) {
        return false;
    }
    return i1.intValue() == i2.intValue();
}

// Considering null is less than not-null
public static int integersCompare(Integer i1, Integer i2) {
    if (i1 == null && i2 == null) {
        return 0;
    }
    if (i1 == null && i2 != null) {
        return -1;
    }
    return i1.compareTo(i2);
}
user_50936160

Because a comparison method has to be done based on type int (x==y) or class Integer (x.equals(y)) with the right operator:

public class Example {

    public static void main(String[] args) {
        int[] arr = {-32735, -32735, -32700, -32645, -32645, -32560, -32560};

        for(int j=1; j<arr.length-1; j++)
            if((arr[j-1] != arr[j]) && (arr[j] != arr[j+1]))
                System.out.println("int>" + arr[j]);

        Integer[] I_arr = {-32735, -32735, -32700, -32645, -32645, -32560, -32560};

        for(int j=1; j<I_arr.length-1; j++)
            if((!I_arr[j-1].equals(I_arr[j])) && (!I_arr[j].equals(I_arr[j+1])))
                System.out.println("Interger>" + I_arr[j]);
    }
}
user_121299770
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