CODEWITHSUNDEEP
java
Ordo
Ordo

Reputation: 705

Comparing to string with each other in Java

I'm looking for a solution to compare two strings with each other. I have already found a few suggestions but i'm not really understanding how to do it. I want to do something like that:

String a = 23;
String b = 2;

if (a < b)
System.out.println("...");
else ..

I've found the compareTo method but i don't get the idea behind it. The code would be something like:

String a = 23;
String b = 2;

if (a.compareTo(b) < 0)
System.out.println("...");
else ..

But why should i compare to strings with each other and then compare it to zero?? I'm really confused.

Upvotes: 2

Views: 869

Answers (6)

124697
124697

Reputation: 21901

Don't use String if you want to use the larger than, smaller than operators. Use int then if you want to change it to string later useInteger.toString(a)

Upvotes: 1

Dainius
Dainius

Reputation: 1862

If you need compare numbers you need override compare() method, because java not allow to override operators. You can use something like this:

public class TestString implements Comparator<String> {
    private static TestString ts = new TestString();
    static public int compareStrings(String s1, String s2) {
        return ts.compare(s1, s2);
    }

    public int compare(String s1, String s2) {
        Integer i1 = Integer.parseInt(s1);
        Integer i2 = Integer.parseInt(s2);
        if (i1 == i2) {
            return 0;
        } else if (i1 < i2) {
            return -1;
        } else {
            return 1;
        }
    }

    static public void main(String[] args) {
        String s1 = "10";
        String s2 = "3";
        if (TestString.compareStrings(s1, s2) < 0) {
            System.out.println("<");
        } else if (TestString.compareStrings(s1, s2) > 0) {
            System.out.println(">");
        }
    }
}

But if you need actually compare values (not for ordering) you look at program design, maybe there need some changes.

Upvotes: 1

fastcodejava
fastcodejava

Reputation: 41117

You cannot do a < b in java with String. You have to use compareTo or Comparator. You cannot write String a = 23; also. You can convert them to integer and then do a < b.

Upvotes: 6

Samuel Parsonage
Samuel Parsonage

Reputation: 3127

Read the API for compareTo 

a.compareTo(b)

The result of this method call:
is a negative number (hence < 0) if a precedes b alphabetically (e.g. a="apple", b="bananna")
is 0 if it is the same string
and is a positive number if a is after b alphabetically

If you want to compare numeric values, either do your comparison on Integers or first parse the strings e.g.

if (Integer.parseInt(a) < Integer.parseInt(b)){
   ...
} else {
 ...
}

Upvotes: 5

Shashi
Shashi

Reputation: 2898

Do like this, it will give the correct result

  String s = "22";
        string s1 = "2";
        string output = "";
        if (s.CompareTo(s1) > 0)
            output = "S is grater";
        else
            output = "s is smaller";

Upvotes: 1

Alnitak
Alnitak

Reputation: 340045

Comparing a and b directly just compares their internal references.

Note (as Jon pointed out) that you can't even use the < operators on Strings, although you can use the == operator.

However to compare their contents use you must use the equals() or comparesTo() methods.

To demostrate the == issues:

public class foobar {
    static public void main(String[] args) {

        // two identical strings
        String a = "foo";
        String b = "foo";

        // and the result of comparing them
        System.out.println(" ==              returns " + (a == b));
        System.out.println(" String.equals() returns " + a.equals(b));

        // append the same string on the end of each
        a += "bar";
        b += "bar";

        // and compare them again
        System.out.println(" ==              returns " + (a == b));
        System.out.println(" String.equals() returns " + a.equals(b));
    }
}

% java foobar
 ==              returns true
 String.equals() returns true
 ==              returns false
 String.equals() returns true

When a and b are both initialised from the same string then string interning initialises both references to look at that immutable string. This means that initially a == b is true.

However as soon as you modify them, even if the contents end up the same, the == test fails.

Upvotes: 1

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