Why Does Comparing Two Java Integer Objects Sometimes Return True?

Introduction

When comparing two Integer objects in Java, the result can be surprising.

Integer a = 100;
Integer b = 100;
System.out.println(a == b); // true

For values outside the cache range the same code prints false:

Integer a = 1000;
Integer b = 1000;
System.out.println(a == b); // false

1. Integer objects and the cache

Integer is the wrapper class for the primitive int. All non‑primitive types are objects that store references.

Java maintains an internal cache (IntegerCache) for the values -128 to 127. When an Integer is created within this range, the same cached object is returned; otherwise a new object is allocated.

Thus, for 100 the two variables reference the same cached object, while for 1000 they reference different objects.

2. Equality comparison

The == operator compares object references, so it returns false for two distinct Integer instances.

To compare the numeric values, use the equals method, which Integer overrides to compare the underlying int values.

Integer a = Integer.valueOf(1000);
Integer b = Integer.valueOf(1000);
System.out.println(a.equals(b)); // true

Summary

Use == to check if two references point to the same object.

Use equals to check if two Integer objects hold the same value.

The Integer cache covers -128 to 127, reducing memory usage for frequently used numbers.