Java: why does `==` return false when comparing two equal strings?

Question

```java
String a = scanner.nextLine(); // user types "yes"
if (a == "yes") {
    System.out.println("ok");
}
```

This never prints "ok" even when I type `yes`.

Accepted Answer

In Java, `==` on objects compares **references** (is it the same object in memory?), not content. The string read from input is a different object from the `"yes"` literal.

Use `.equals()`:

```java
if ("yes".equals(a)) { ... }            // null-safe order
if ("yes".equalsIgnoreCase(a.trim())) { ... }
```

Putting the literal first avoids a `NullPointerException` when `a` is `null`. `==` sometimes *seems* to work with literals because of string interning, which is why the bug is so confusing.

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