The Magic of 128 in Java: Understanding Integer Caching

The Integer class is essentially just an ordinary Java class — even if the values are the same, they are different objects.

For example:

        Integer a = <span class="hljs-number">148</span>;
        Integer b = <span class="hljs-number">148</span>;
        System.out.println(a==b);`

The output here is false. Easy to understand.

However, if you change the value to a number below 128, such as 48:

<pre class="prettyprint">`        Integer a = <span class="hljs-number">48</span>;
        Integer b = <span class="hljs-number">48</span>;
        System.out.println(a==b);`</pre>

You’ll find the output becomes true. The reason is that the JDK caches integers below 128. When you declare two Integer objects with the value 48, they actually point to the same location in memory.

Of course, you can also explicitly create a new Integer object:

<pre class="prettyprint">`        Integer a = <span class="hljs-number">48</span>;
        Integer b = <span class="hljs-keyword">new</span> Integer(<span class="hljs-number">48</span>);
        System.out.println(a==b); 

The output here becomes false.

Source: https://lichuanyang.top/en/posts/64970/