How to concatenate characters in java?

问题

How do you concatenate characters in java? Concatenating strings would only require a + between the strings, but concatenating chars using + will change the value of the char into ascii and hence giving a numerical output. I want to do System.out.println(char1+char2+char3... and create a String word like this.

I could do

System.out.print(char1);
System.out.print(char2);
System.out.print(char3);

But, this will only get me the characters in 1 line. I need it as a string. Any help would be appreciated.

Thanks

回答1:

Do you want to make a string out of them?

String s = new StringBuilder().append(char1).append(char2).append(char3).toString();

Note that

String b = "b";
String s = "a" + b + "c";

Actually compiles to

String s = new StringBuilder("a").append(b).append("c").toString();

Edit: as litb pointed out, you can also do this:

"" + char1 + char2 + char3;

That compiles to the following:

new StringBuilder().append("").append(c).append(c1).append(c2).toString();

Edit (2): Corrected string append comparison since, as cletus points out, a series of strings is handled by the compiler.

The purpose of the above is to illustrate what the compiler does, not to tell you what you should do.

回答2:

I wasn't going to answer this question but there are two answers here (that are getting voted up!) that are just plain wrong. Consider these expressions:

String a = "a" + "b" + "c";
String b = System.getProperty("blah") + "b";

The first is evaluated at compile-time. The second is evaluated at run-time.

So never replace constant concatenations (of any type) with StringBuilder, StringBuffer or the like. Only use those where variables are invovled and generally only when you're appending a lot of operands or you're appending in a loop.

If the characters are constant, this is fine:

String s = "" + 'a' + 'b' + 'c';

If however they aren't, consider this:

String concat(char... chars) {
  if (chars.length == 0) {
    return "";
  }
  StringBuilder s = new StringBuilder(chars.length);
  for (char c : chars) {
    s.append(c);
  }
  return s.toString();
}

as an appropriate solution.

However some might be tempted to optimise:

String s = "Name: '" + name + "'"; // String name;

into this:

String s = new StringBuilder().append("Name: ").append(name).append("'").toString();

While this is well-intentioned, the bottom line is DON'T.

Why? As another answer correctly pointed out: the compiler does this for you. So in doing it yourself, you're not allowing the compiler to optimise the code or not depending if its a good idea, the code is harder to read and its unnecessarily complicated.

For low-level optimisation the compiler is better at optimising code than you are.

Let the compiler do its job. In this case the worst case scenario is that the compiler implicitly changes your code to exactly what you wrote. Concatenating 2-3 Strings might be more efficient than constructing a StringBuilder so it might be better to leave it as is. The compiler knows whats best in this regard.

回答3:

If you have a bunch of chars and want to concat them into a string, why not do

System.out.println("" + char1 + char2 + char3);

回答4:

You can use the String constructor.

System.out.println(new String(new char[]{a,b,c}));

回答5:

You need to tell the compiler you want to do String concatenation by starting the sequence with a string, even an empty one. Like so:

System.out.println("" + char1 + char2 + char3...);

回答6:

System.out.println(char1+""+char2+char3)

String s = char1+""+char2+char3;

回答7:

You need a String object of some description to hold your array of concatenated chars, since the char type will hold only a single character. e.g.,

StringBuilder sb = new StringBuilder('a').append('b').append('c');
System.out.println(sb.toString);

回答8:

public class initials {

public static void main (String [] args) {

    char initialA = 'M';
    char initialB = 'P';
    char initialC = 'T';

    System.out.println("" + initialA + initialB + initialC );


}

}

回答9:

I don't really consider myself a Java programmer, but just thought I'd add it here "for completeness"; using the (C-inspired) String.format static method:

String s = String.format("%s%s", 'a', 'b'); // s is "ab"

回答10:

this is very simple approach to concatenate or append the character

       StringBuilder desc = new StringBuilder(); 
       String Description="this is my land"; 
       desc=desc.append(Description.charAt(i));

回答11:

simple example to selecting character from string and appending to string variable

private static String findaccountnum(String holdername, String mobile) {

    char n1=holdername.charAt(0);
    char n2=holdername.charAt(1);
    char n3=holdername.charAt(2);
    char n4=mobile.charAt(0);
    char n5=mobile.charAt(1);
    char n6=mobile.charAt(2);
    String number=new StringBuilder().append(n1).append(n2).append(n3).append(n4).append(n5).append(n6).toString();

    return number;
}

回答12:

System.out.print(a + "" + b + "" + c);

来源：https://stackoverflow.com/questions/328249/how-to-concatenate-characters-in-java

标签

java

character

concatenation