如何在 Java 中退出 while 循环？

Use break:

while (true) {
....
if (obj == null) {
break;
}
....
}

However, if your code looks exactly like you have specified you can use a normal while loop and change the condition to obj != null:

while (obj != null) {
....
}

Take a look at the Java™ Tutorials by Oracle.

But basically, as dacwe said, use break.

If you can it is often clearer to avoid using break and put the check as a condition of the while loop, or using something like a do while loop. This isn't always possible though.

while(obj != null){
// statements.
}

break is what you're looking for:

while (true) {
if (obj == null) break;
}

alternatively, restructure your loop:

while (obj != null) {
// do stuff
}

or:

do {
// do stuff
} while (obj != null);

Finding a while...do construct with while(true) in my code would make my eyes bleed. Use a standard while loop instead:

while (obj != null){
...
}

And take a look at the link Yacoby provided in his answer, and this one too. Seriously.

The while and do-while Statements

You can do multiple condition logical tests within the while() check using the same rules as within any logical check.

while ( obj != null ) {
// do stuff
}

works, as does

while ( value > 5 && value < 10 ) {
// do stuff
}

are valid. The conditionals are checked on each iteration through the loop. As soon as one doesn't match, the while() loop is exited. You can also use break;

while ( value > 5 ) {
if ( value > 10 ) { break; }
...
}

You can use "break", already mentioned in the answers above. If you need to return some values. You can use "return" like the code below:

 while(true){
if(some condition){
do something;
return;}
else{
do something;
return;}
}

in this case, this while is in under a method which is returning some kind of values.

if you write while(true). its means that loop will not stop in any situation for stop this loop you have to use break statement between while block.

package com.java.demo;


/**
* @author Ankit Sood Apr 20, 2017
*/
public class Demo {


/**
* The main method.
*
* @param args
*            the arguments
*/
public static void main(String[] args) {
/* Initialize while loop */
while (true) {
/*
* You have to declare some condition to stop while loop


* In which situation or condition you want to terminate while loop.
* conditions like: if(condition){break}, if(var==10){break} etc...
*/


/* break keyword is for stop while loop */


break;
}
}
}

You can use "break" to break the loop, which will not allow the loop to process more conditions

To exit a while loop, use Break; This will not allow to loop to process any conditions that are placed inside, make sure to have this inside the loop, as you cannot place it outside the loop