I want to send a string to a method and change the string there. The method should return void. Example:
String s = "Hello";
ChangeString(s);
String res = s;
//res = "HelloWorld"
-------------------------------------------
private void ChageString(String s){
s = s + "World";
}
How can I do it in Java? Can it be done without adding another class?
Thanks! PB
Your method cannot work with the current interface because of two reasons:
s in your method it only modifies the local s, not the original s in the calling code.To make your method work you need to change the interface. The simplest change is to return a new string:
private String changeString(String s){
return s + "World";
}
Then call it like this:
String s = "Hello";
String res = changeString(s);
See it working online: ideone
Use StringBuffer instead of String it will solve your problem.
public static void main(String[] args) {
StringBuffer s = new StringBuffer("Hello");
changeString(s);
String res = s.toString();
//res = "HelloWorld"
}
private static void changeString(StringBuffer s){
s.append("World");
}
Or if you really need to use only String so here is the solution using reflection:
public static void main(String[] args) {
String s = "Hello";
changeString(s);
String res = s;
//res = "HelloWorld"
}
private static void changeString(String s){
char[] result = (s+"World").toCharArray();
try {
Field field = s.getClass().getDeclaredField("value");
field.setAccessible(true);
field.set(s, result);
} catch (NoSuchFieldException | SecurityException | IllegalArgumentException |
IllegalAccessException e1) {
e1.printStackTrace();
}
}
Nope, can't be done while returning void.
Java passes parameters by value. Strings are immutable, so you can't change its value. You're out of luck.
You can do this:
private String changeString(String original) {
return original + " World";
}
You could wrap up your string in an object:
public class StringWrapper {
String _str;
public StringWrapper(String str) { set(str); }
public void set(String str) { _str = str; }
public String toString() { return _str; }
}
Allowing you to do:
StringWrapper s = new StringWrapper("Hello");
ChangeString(s);
String res = s + "";
//res = "HelloWorld"
private void ChageString(StringWrapper s) {
s.set(s + "World");
}
No, a Java String is immutable and cannot be changed. You can just return a new String and assign it to the same variable.
Even further: String is declared as final, so you can't extend String to add new behaviour
Use the StringBuffer/StringBuilder to change the string. Strings in java are immutable, this means that once they are assigned a value, they cannot be changed, the code that seems to be changing the string actually makes a new object. Here's something on string buffer, hope it helps. :)
is it acceptable?
//solution1:
private static void ChangeString(String[] s){
s[0] = s[0] + "World";
}
public static void main(String[] args)
{
String[] s = new String[]{"Hello"};
ChangeString(s);
String res = s[0];
System.out.println(res);
}
//solution2:
class Container {
public Container(String value) {
this.value = value;
}
public String value;
}
public class Main{
private static void ChangeString(Container s) {
s.value = s.value + "World";
}
public static void main(String[] args) {
Container s = new Container("hello");
ChangeString(s);
String res = s.value;
System.out.println(res);
}
}
