reformatting java code problem

hello, i would really apreciate any help on this one.. i have just started file i/o in java and already the homework is bugging me.
I am to write a program that reformats java source code from the next-line brace style to the end-of-line brace style. for example the following code :

Code Java:

---

public class Test
{
      public static void main(String[] args)
     {
       // some statements
     }
 
}

---

would be reformatted to :

Code Java:

---

 
public class Test{
      public static void main(String[] args){
       // some statements
      }
 
}

---

my attempted code so far is below.. i don't know if i can use concat() in this instance and if i am even doing anything right... please help.. thanks.

Code Java:

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import java.io.*;
import java.util.*;
 
public class Main {
 
	public static void main(String[] args) throws Exception {
 
		File file = new File("C:\\JackTest\\test.txt");
		format(file);
 
	}
 
	public static void format(File f) throws Exception {
 
		Scanner input = new Scanner(f);
 
		String[] lines = new String[7];
 
		while (input.hasNext()) {
 
			for (int i = 0; i < 7; i++) {
 
				lines[i] = input.nextLine();
 
				if (lines[i].startsWith("{")) {
 
					lines[i-1].concat("{");
					// i am stuck here.. 
 
				}
 
 
 
			}
 
		}
	}
}

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