An Interesting Interview Question: What’s the Difference Among new Integer(“127”), Integer.valueOf(“127”) and Integer.valueOf(“128”)?

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Did you think it was so easy when you saw this question? I wonder if you can answer it easily. 😊

Actually, this question involves a subtlety in the creation and caching mechanism of the Integer object in Java. It’s a seemingly basic problem but is easy to overlook.

First of all, let’s take a look at a piece of code and then conduct a specific analysis.

Integer a = new Integer("127");
Integer b = new Integer("127");
System.out.println(a == b);  // false

Integer c = Integer.valueOf("127");
Integer d = Integer.valueOf("127");
System.out.println(c == d);  // true

Integer e = Integer.valueOf("128");
Integer f = Integer.valueOf("128");
System.out.println(e == f);  // false

Main Differences

1. Object Creation

Both new Integer and Integer.valueOf methods will create new objects.

However, new Integer will create a new object every time, while Integer.valueOf will create an object based on the cache hit situation.