使用“ while（line = reader.readLine（）！= null）”时，类型不匹配

Question

So I am trying to simply print each line of my buffered read to see if It is outputting correctly but I am getting an error in eclipse and at runtime. Absolutely everywhere I look the code for outputting buffered reader is

    String line;
    while(line = myReader.readLine() != null){
    {
        System.out.println(line);
    }

This throws an error saying that "Type mismatch cannot convert from boolean to string." If I change line to a boolean variable it runs and prints "true" three times which is how many lines I am expecting, so does anyone have any idea how I can print the actual text? I am assuming it is throwing the error because != null will return true or false but I cannot get it to work.

Answer 1

This is because higher Operator Precedence of equality v/s assignment

From the Documentation :

When operators of equal precedence appear in the same expression, a rule must govern which is evaluated first. All binary operators except for the assignment operators are evaluated from left to right; assignment operators are evaluated right to left.

(emphasis mine) So

line = myReader.readLine() != null

Gets evaluated as per precedence as

line = (myReader.readLine() != null)

which is an attempt to assign boolean to line , giving the error.

Correct usage:

(line = myReader.readLine()) != null

Answer 2

while ( (line = myReader.readLine()) != null ) { will do. you forgot to put () correctly.

The problem was, myReader.readLine() != null part was evaluated first.