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fix(guide): Fix incorrect code in Java Strings (#27399)

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Using `==` to compare String objects checks references to the two objects, and in this case, those two references point to the same string object created **in the String Pool**. Hence this returns `true`, and not `false`, as is incorrectly stated in the guide.

Also fixed formatting.
This commit is contained in:
Manish Giri
2018-10-24 06:28:32 -04:00
committed by mrugesh mohapatra
parent 816036dba6
commit 164f165fca
1 changed files with 12 additions and 11 deletions
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23
guide/english/java/strings/index.md
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@ -3,7 +3,7 @@ title: Strings
--- ---
# Strings # Strings
Strings are sequences of characters. In Java, a `String` is an `Object`. Strings should not be confused with `char` as characters are literally 1 value rather than a sequence of characters. You can still use 1 value within a String, however it is preferred to use `char` when you are checking for 1 character. Strings are sequences of characters. In Java, a `String` is an `Object`. Strings should not be confused with `char` as characters are literally a single value rather than a sequence of characters. You can still use a single value within a String, however, it is preferred to use `char` when you are checking for a single character.
```java ```java
String course = "FCC"; String course = "FCC";
@ -37,7 +37,7 @@ String str2 = "This is a string";
String str3 = new String("This is a string"); String str3 = new String("This is a string");
``` ```
The answer is: 2 String objects are created. `str` and `str2` both refer to the same object. `str3` has the same content but using `new` forced The answer is: **2** String objects are created. `str` and `str2` both refer to the same object. `str3` has the same content but using `new` forced
the creation of a new, distinct, object. the creation of a new, distinct, object.
When you create a String literal, the JVM internally checks, what is known as the `String pool`, to see if it can find a similar (content wise) When you create a String literal, the JVM internally checks, what is known as the `String pool`, to see if it can find a similar (content wise)
@ -62,16 +62,16 @@ public class StringExample{
char ch[] = {'s','t','r','i','n','g','s'}; char ch[] = {'s','t','r','i','n','g','s'};
String s2 = new String(ch); // converting char array to string String s2 = new String(ch); // converting char array to string
String s3 = new String("example"); // creating Java string by new keyword String s3 = new String("example"); // creating Java string by new keyword
System.out.println(s1); System.out.println(s1); // prints "java"
System.out.println(s2); System.out.println(s2); // prints "strings"
System.out.println(s3); System.out.println(s3); // prints "example"
} }
} }
``` ```
#### Comparing Strings #### Comparing Strings
If you want to compare the value of two String variables, you can't use ==. This is due to the fact that this will compare the references of the variables If you want to compare the value of two String variables, you can't use `==`. This is due to the fact that this will compare the references of the variables
and not the values that are linked to them. To compare the stored values of the Strings you use the method equals. and not the values that are linked to them. To compare the stored values of the Strings you use the `.equals()` method.
```java ```java
boolean equals(Object obj) boolean equals(Object obj)
@ -82,12 +82,13 @@ It returns true if two objects are equal and false otherwise.
String str = "Hello world"; String str = "Hello world";
String str2 = "Hello world"; String str2 = "Hello world";
System.out.println(str == str2); // This prints false System.out.println(str == str2); // This prints true
System.out.println(str.equals(str2); // This prints true System.out.println(str.equals(str2)); // This prints true
``` ```
The first comparison is false because "==" looks at the references and they aren't the same. The first comparison is true because "==" looks at the references and they are the same, because the JVM simply returns a reference
to the same `"Hello world"` object created in the String Pool the first time.
The second comparison is true because the variables store the same values. In this case "Hello world". The second comparison is true because the variables store the same values. In this case - `"Hello world"`.
We have several inbuilt methods in String. The following is an example of the String Length() method . We have several inbuilt methods in String. The following is an example of the String Length() method .