What is the exact difference between out.write() a

问题:

In my servlet I gave both out.print and out.write. but both prints in the browser.

What is the exact difference between these two and when to use out.print and out.write ?

回答1:

The basic difference is that out.write() explodes if you pass it a null:

String s = null;
out.print(s); // outputs the text "null"
out.write(s); // NullPointerException

回答2:

PrintWriter:

public void write(String s)

Write a string. This method cannot be inherited from the Writer class because it must suppress I/O exceptions.

print method has higher level of abstraction.

public void print(String s)

Print a string. If the argument is null then the string "null" is printed. Otherwise, the string's characters are converted into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of the write(int) method.

Hope this helps.

回答3:

There are three major differences:

1) If you try to print a null value of a String with out.write() , It will throw NullPointerException while out.print() will simply print NULL as a string.

 String name = null;
 out.write(name); // NullPointerException
 out.print(name); // 'Null' as text will be printed

2) out.print() can print Boolean values but out.write() can not.

boolean b = true;
out.write(b); // Compilation error
out.print(b); // 'true' will be printed 

3) If you are using out.write(), you simply can not place arithmetic operation code but out.print() provides the support.

out.write(10+20); // No output will be displayed.
out.print(10+20); // Output '30' will be displayed. 

回答4:

The out variable in your case is most likely refers to a PrintWriter

Just compare the description of write...

public void write(String s)

Write a string. This method cannot be inherited from the Writer class because it must suppress I/O exceptions.

... with the description of println ...

public void println(String x)

Print a String and then terminate the line. This method behaves as though it invokes print(String) and then println().

... and print ...

public void print(String s)

Print a string. If the argument is null then the string "null" is printed. Otherwise, the string's characters are converted into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of the write(int) method.

All in all I'd say that the print methods work on a higher level of abstraction and is the one I prefer to work with when writing servlets.

回答5:

PrintWriter's implementation communicates the difference better than javadoc

public void print(String s) {
    if (s == null) {
        s = "null";
    }
    write(s);
}

回答6:

I simply know it as like this:

out.println() is method of javax.​servlet.​jsp.​JspWriter

out.write() is method of java.io.Writer

回答7:

First thing is you can't use javax.​servlet.​jsp.​JspWriter out in a servlet. It has to be used in a .jsp file, because out is a method local variable in _jspService(...) method of your .jsp file.

There is no difference in the purpose of using out.print() and out.write(). Both are used to write the String version of the given object to JspWriter's buffer.

However, JspWriter.print() is capable of taking many types of arguments than Writer.write().

JspWriter.print()

• Object
• String
• boolean
• char
• char[]
• double
• float
• int
• long

Writer.write()

• String
• char
• int

回答8:

write() method only writes characters to stream(or console) but does not print, while print() method writes and print it on stream (or console).

System.out.write(97);
System.out.print('j');

first statement writes character 97 i.e 'a' on console but does not print, while second statement prints 'a' which is written already on stream and 'j' which is passed in print() method.

回答9:

out.write(-) vs out.print(-)

One more difference is out.write(-) method just write data or object to browser like a file. You can not write any statement like out.write(10*20); but we do this with out.print(10*20);