无法在Java中解析lineSeparator

获取错误：无法解析“系统”中的方法“lineSeparator”。是因为我的java版本太低，或者需要导入任何库才能使用lineSeparator。Thx。您使用的是哪个java版本？

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System.lineSeparator（）

绝对是在1.7中添加的，谢谢回复！是的，我使用的是1.6版本，这就是我出错的原因。谢谢你的帮助！

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class Main {
public static void main(String args[]) throws IOException {
    //Instantiating the File class
    String filePath = "Data.txt";
    //Instantiating the Scanner class to read the file
    Scanner sc = new Scanner(new File(filePath));
    //instantiating the StringBuffer class
    StringBuffer buffer = new StringBuffer();
    //Reading lines of the file and appending them to StringBuffer
    while (sc.hasNextLine()) {
        buffer.append(sc.nextLine()+System.lineSeparator());
    }
    String fileContents = buffer.toString();
    //closing the Scanner object
    sc.close();
    String oldLine = "No_Assessment";
    String newLine = "Yes_Assessment";
    //Replacing the old line with new line
    fileContents = fileContents.replaceAll(oldLine, newLine);
    //instantiating the FileWriter class
    FileWriter writer = new FileWriter(filePath);
    writer.append(fileContents);
    writer.flush();
}
}