learning java 推回输入流

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.PushbackReader;

public class PushbackTest {
    public static void main(String[] args) {
        try {
            var pr = new PushbackReader(new FileReader("src/com/company/PushbackTest.java"),64);
            {
                var buf = new char[32];
                var lastContent = "";
                var hasRead = 0;

                while ((hasRead = pr.read(buf)) > 0){
                    var content = new String(buf,0 ,hasRead);
                    var targetIndex = 0;
                    if ((targetIndex = (lastContent + content).indexOf("new PushbackReader")) > 0){

                        pr.unread((lastContent+content).toCharArray());

                        if (targetIndex >  32){
                            buf = new char[targetIndex];
                        }
                        pr.read(buf,  0 , targetIndex);
                        System.out.println(new String(buf,0, targetIndex));
                        System.exit(0);
                    }
                    else {
                        System.out.println(lastContent);
                        lastContent = content;
                    }
                }
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

output:

package com.company;

import j
ava.io.FileNotFoundException;
i
mport java.io.FileReader;
impor
t java.io.IOException;
import j
ava.io.PushbackReader;

public
 class PushbackTest {
    publi
c static void main(String[] args
) {
        try {
            var pr =