EN
Java - compare strings
3 points
One of the most common problem that affects new Java Developers is how to compare two String objects. They try to compare strings with == operator what makes only reference comparision - not values. To solve this problem equals method should be used. This article explains how to compare two strings.
xxxxxxxxxx1
public class Program {2
3
public static void main(String[] args) {4
5
String a = "text 1";6
String b = "text 1";7
String c = "text 2";8
9
// CORRECT WAY OF VALUES COMPARISON:10
11
System.out.println(a.equals(b)); // true12
System.out.println(a.equals(c)); // false13
14
// good practice because of literal on left site15
// NullPoiterException will not occur if a or c variables will be null16
System.out.println("text 1".equals(a)); // true17
System.out.println("text 1".equals(c)); // false18
19
System.out.println("text 1".equals("text 1")); // true20
System.out.println("text 2".equals("text 1")); // false21
22
// BAD PRACTICE BECAUSE OF VARIABLE ON LEFT SITE AND LITERAL ON RIGHT SITE:23
24
// possible NullPoiterException if a or c variable will be null25
System.out.println(a.equals("text 1")); // true 26
System.out.println(c.equals("text 1")); // false27
}28
}29
Note: this approach is available sice java 1.7.
Output:
xxxxxxxxxx1
true2
false3
true4
false5
true6
false7
true8
falsexxxxxxxxxx1
import java.util.Objects;2
3
public class Program {4
5
public static void main(String[] args) {6
7
String a = "text 1";8
String b = "text 1";9
String c = "text 2";10
11
System.out.println(Objects.equals(a, b)); // true12
System.out.println(Objects.equals(a, c)); // false13
System.out.println(Objects.equals(b, a)); // true14
System.out.println(Objects.equals(c, a)); // false15
16
System.out.println(Objects.equals(a, "text 1")); // true17
System.out.println(Objects.equals("text 1", b)); // true18
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System.out.println(Objects.equals("text 1", "text 1")); // true20
System.out.println(Objects.equals("text 1", "text 2")); // false21
}22
}Output:
xxxxxxxxxx1
true2
false3
true4
false5
true6
true7
true8
falsexxxxxxxxxx1
public class Program {2
3
public static void main(String[] args) {4
5
String a = "text 1";6
String b = "text 1";7
String c = "text 2";8
9
// INCORRECT WAY OF VALUES COMPARISON:10
11
// this examples return true because of reference to same object in memory12
System.out.println(a == b); // true13
System.out.println("text 1" == "text 1"); // true14
}15
}Output:
xxxxxxxxxx1
true2
trueNote: for all
"text 1"occurrences java uses same object in memory what caused true result during references comparison with==operator.
