Java add chars to a string

Question

I have two strings in a java program, which I want to mix in a certain way to form two new strings. To do this I have to pick up some constituent chars from each string and add them to form the new strings. I have a code like this(this.eka and this.toka are the original strings):

String muutettu1 = new String();
String muutettu2 = new String();
muutettu1 += this.toka.charAt(0) + this.toka.charAt(1) + this.eka.substring(2);
muutettu2 += this.eka.charAt(0) + this.eka.charAt(1) + this.toka.substring(2);
System.out.println(muutettu1 + " " + muutettu2);

I'm getting numbers for the .charAt(x) parts, so how do I convert the chars to string?

As your example shows, you can also use substring to return a String directly. Any reason why you are using both charAt and substring in the same statement? — JRL
– JRL, Commented Oct 31, 2009 at 14:39

alphazero · Accepted Answer · 2009-10-31 14:42:16Z

15

StringBuilder builder = new StringBuilder();
builder
   .append(this.toka.charAt(0))
   .append(this.toka.charAt(1))
   .append(this.toka.charAt(2))
   .append(' ')  
   .append(this.eka.charAt(0))
   .append(this.eka.charAt(1))
   .append(this.eka.charAt(2));
System.out.println (builder.toString());

answered Oct 31, 2009 at 14:42

alphazero

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5 Comments

Thomas Jung Over a year ago

I think, your result will be wrong. subString(2) is the string beginning with the index 2.

alphazero Over a year ago

Yep, I missed that. Regardless, append is an overloaded method and you can pass it Strings as well. The salient point here was to not use String directly and use StringBuilder (or StringBuffer if on older JRE) to minimize the performance cost.

Thomas Jung Over a year ago

a + b will be compiled to new StringBuilder().append(a).append(b).toString() anyway.

user1610406 Over a year ago

I really like this answer, but why not an enhanced for loop? eg. for(String i : this.toka) and do the same for this.eka

alphazero Over a year ago

Try javap on both variants. (Haven't done it myself, but) likely the iterative form will peform superflous allocations for the 2 control structures (possibly unrolled by the compiler). Also do note that OP's Q did not indicate that the source Strings actually terminate at the indices provided, so it will need to be an explicit for loop form.

JAYD3V · Accepted Answer · 2021-09-06 01:34:13Z

7

Just use always use substring() instead of charAt()

In this particular case, the values are mutable, consequently, we can use the built in `String` class method `substring()` to solve this problem (@see the example below):

Example specific to the OP's use case:


    muutettu1 += toka.substring(0,1) + toka.substring(1,2) + eka.substring(2);
   
    muutettu2 += eka.substring(0,1) + eka.substring(1,2) + toka.substring(2);

Concept Example, (i.e Example showing the generalized approach to take when attempting to solve a problem using this concept)


    muutettu1 += toka.substring(x,x+1) + toka.substring(y,y+1) + eka.substring(z);

    muutettu2 += eka.substring(x,x+1) + eka.substring(y,y+1) + toka.substring(z);

"...Where x,y,z are the variables holding the positions from where to extract."

edited Sep 6, 2021 at 1:34

JAYD3V

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answered Oct 31, 2009 at 14:39

jitter

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Comments

Thomas Jung · Accepted Answer · 2009-10-31 14:47:42Z

7

The obvious conversion method is Character.toString.

A better solution is:

String muutettu1 = toka.substring(0,2) + eka.substring(2);
String muutettu2 = eka.substring(0,2) + toka.substring(2);

You should create a method for this operation as it is redundant.

The string object instatiantiation new String() is unnecessary. When you append something to an empty string the result will be the appended content.

edited Oct 31, 2009 at 14:47

answered Oct 31, 2009 at 14:34

Thomas Jung

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Comments

htlbydgod · Accepted Answer · 2017-09-13 05:18:05Z

0

You can also convert an integer into a String representation in two ways: 1) String.valueOf(a) with a denoting an integer 2) Integer.toString(a)

answered Sep 13, 2017 at 5:18

htlbydgod

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Comments

Chàrìthà SG · Accepted Answer · 2015-06-08 18:38:47Z

-2

This thing can adding a chars to the end of a string

StringBuilder strBind = new StringBuilder("Abcd");
strBind.append('E');
System.out.println("string = " + str);
//Output => AbcdE
str.append('f');
//Output => AbcdEf

answered Jun 8, 2015 at 18:38

Chàrìthà SG

11 bronze badge

3 Comments

Friedrich Over a year ago

What is this? Where does str come from? What are you even doing?

Alex Liu 33214 Over a year ago

What is this? you didn't even declare what str was yet!

JAYD3V Over a year ago

You answered this question with JavaScript lol. This is a question that references JAVA, a totally different language.

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In this particular case, the values are mutable, consequently, we can use the built in `String` class method `substring()` to solve this problem (@see the example below):

Example specific to the OP's use case:

Concept Example, (i.e Example showing the generalized approach to take when attempting to solve a problem using this concept)

"...Where x,y,z are the variables holding the positions from where to extract."

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In this particular case, the values are mutable, consequently, we can use the built in String class method substring() to solve this problem (@see the example below):

Example specific to the OP's use case:

Concept Example, (i.e Example showing the generalized approach to take when attempting to solve a problem using this concept)

"...Where x,y,z are the variables holding the positions from where to extract."

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In this particular case, the values are mutable, consequently, we can use the built in `String` class method `substring()` to solve this problem (@see the example below):