# Java String Comparison: equals vs == Explained

> Compare strings in Java using equals(), equalsIgnoreCase(), and compareTo() methods, with an explanation of why the == operator gives unreliable results

**URL:** https://sentry.io/answers/how-to-compare-strings-in-java/

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## The Problem

How do I compare strings in Java?

## The Solution

To compare strings in Java for equality, you should use `String.equals()`.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = "java";
        String str2 = "java";
        System.out.println(str1.equals(str2));
    }
}
```

Output:

```
true
```

If uppercase and lowercase difference isn't important, you can use `String.equalsIgnoreCase()`.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = "java";
        String str2 = "Java";
        System.out.println(str1.equalsIgnoreCase(str2));
    }
}
```

Output:

```
true
```

If you want to find out if a String is "bigger" or "smaller" than another string (that is, whether it comes before or after alphabetically), use `String.compareTo()`.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = "aaa";
        String str2 = "bbb";
        String str3 = "ccc";
        String str4 = "bbb";
        System.out.println(str2.compareTo(str3));
        System.out.println(str2.compareTo(str1));
        System.out.println(str2.compareTo(str4));
    }
}
```

Output:

```
-1
1
0
```

The first output is `-1`, indicating that `str2` (`"bbb"`) comes **before** `str3` (`"ccc"`).

The second output is `1`, indicating that `str2` (`"bbb"`) comes **after** `str1` (`"aaa"`).

The third output is `0`, indicating that `str2` (`"bbb"`) is equal to `str4` (`"bbb"`).

### Why you shouldn't use `==` for string comparison

Strings in Java are stored on the heap, and the variable only stores a **reference** to where the real string value can be found.

If you use `==` to compare strings, you might get unexpected results.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = new String("java");
        String str2 = new String("java");
        System.out.println(str1 == str2);
    }
}
```

Output:

```
false
```

Here, the two strings have equal values but these values are not stored in the variables `str1` and `str2`.

When dealing with primitive types like `int`, any variables with the same value will also have the same identity code. But when dealing with non-primitive types like String, this is not the case.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = new String("java");
        String str2 = new String("java");
        int int1 = 1;
        int int2 = 1;

        System.out.println(System.identityHashCode(int1));
        System.out.println(System.identityHashCode(int2));

        System.out.println(System.identityHashCode(str1));
        System.out.println(System.identityHashCode(str2));
    }
}
```

Output:

```
808993268
808993268
1229416514
2016447921
```

What makes this confusing is that often `==` will return `true` if you compare two strings with the same value. In the code above we used `new String("java")` to create two separate strings, but if we create the strings without the explicit `new` keyword, Java will do some optimization in the background and only store the string once.

```java
public class Main {

    public static void main(String[] arg) {
        String str1 = "java";
        String str2 = "java";

        System.out.println(System.identityHashCode(str1));
        System.out.println(System.identityHashCode(str2));

        // do not do this
        System.out.println(str1 == str2);
    }
}
```

Here, the two strings have the same hashcode, and `==` will tell you that they are the same string. This is a side effect of Java's memory optimization and shouldn't be relied on, as it may not always behave consistently.

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*Source: [sentry.io/answers/how-to-compare-strings-in-java/](https://sentry.io/answers/how-to-compare-strings-in-java/)*