‍java字符流将文件t1.txt和文件t2.txt的内容读取并输出；将t1.txt和t2.txt的内容合并到新的t3.txt中；输出文件t3.txt的内容。

以下是Java代码实现：

import java.io.*;

public class MergeFilesDemo {
    public static void main(String[] args) {
        try {
            // 读取文件t1.txt
            FileReader reader1 = new FileReader("t1.txt");
            BufferedReader br1 = new BufferedReader(reader1);
            String line1 = br1.readLine();
            while (line1 != null) {
                System.out.println(line1);
                line1 = br1.readLine();
            }
            br1.close();
            reader1.close();
            
            // 读取文件t2.txt
            FileReader reader2 = new FileReader("t2.txt");
            BufferedReader br2 = new BufferedReader(reader2);
            String line2 = br2.readLine();
            while (line2 != null) {
                System.out.println(line2);
                line2 = br2.readLine();
            }
            br2.close();
            reader2.close();
            
            // 合并文件t1.txt和t2.txt到t3.txt
            FileWriter writer = new FileWriter("t3.txt");
            FileReader reader3 = new FileReader("t1.txt");
            BufferedReader br3 = new BufferedReader(reader3);
            String line3 = br3.readLine();
            while (line3 != null) {
                writer.write(line3);
                writer.write("\n"); // 换行
                line3 = br3.readLine();
            }
            br3.close();
            reader3.close();
            
            FileReader reader4 = new FileReader("t2.txt");
            BufferedReader br4 = new BufferedReader(reader4);
            String line4 = br4.readLine();
            while (line4 != null) {
                writer.write(line4);
                writer.write("\n"); // 换行
                line4 = br4.readLine();
            }
            br4.close();
            reader4.close();
            
            writer.close();
            
            // 读取文件t3.txt
            FileReader reader5 = new FileReader("t3.txt");
            BufferedReader br5 = new BufferedReader(reader5);
            String line5 = br5.readLine();
            while (line5 != null) {
                System.out.println(line5);
                line5 = br5.readLine();
            }
            br5.close();
            reader5.close();
            
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

上述代码会依次读取文件t1.txt和t2.txt的内容并输出，然后将这两个文件的内容合并到新的t3.txt文件中，并最后输出文件t3.txt的内容。