Java??? ?? ??? ???(?? ??? ???)? ??? ? StringBuilder? StringBuffer ??? ???? ? ?? ????. ? ? ?? ?? ??? ? ?? ?? ??? ?????? ??? ???, ?? ? ?????? ???? ?? ????. ????? ? ??? ??? ???? ? ??? ?? ???? ??? ???? ?? ?? ??? ?????.

?? ???: StringBuilder? StringBuffer

? ??? ? ? ??? ???????.

1. StringBuilder: ?? ??? ??? ?? ???? ??

• StringBuilder? ?? ??? ??????. ?, ?? ???? ??? ? ????.

• ???? ???? ????. ??? ?? ??? ????? ??????.

• ????? ??: StringBuilder? ??? ????? ?? ??? StringBuffer?? ????.

• ?? ??? ??: ?? ?? ?? ?? ?? ??? ???? StringBuilder? ???? ?? ?? ? ?? ??? ??? ??? ? ????.

?: StringBuilder?? ???? ??? ??

? ???? ? ?? ???? ???? StringBuilder ????? ??? ?????. ??? ??? ???? ?? ?? ??? ?????.

public class StringBuilderBasics {

    public void threadUnsafe() {
        // Common resource being shared
        StringBuilder builder = new StringBuilder();

        // Thread appending "A" 1000 times
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                builder.append("A");
            }
        });

        // Thread appending "B" 1000 times
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                builder.append("B");
            }
        });

        t1.start();
        t2.start();

        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // Result: 1840 (unpredictable)
        System.out.println("Length: " + builder.toString().length());
    }

    public static void main(String[] args) {
        new StringBuilderBasics().threadUnsafe();
    }
}

??:

• ??? ????? ?? StringBuilder ??? ?? ??? ??? ? ????(?: 2000 ?? 1840 ).

• ?? ? ???? ??? ?? ??? ???? ???? ?? ?? ??? ???? ??? ?????.

??: ?? ??? ???? ??? ???? ???? ???? ???? StringBuilder? ?????.

2. StringBuffer: ????? ??? ?? ??? ??

• StringBuffer? ?? ???? ???? ??? ? ????.

• ????? ??? ?????.

• ??? ???? ??? ?? ??? ??? ??????.

• ?? ??: ???? ?? ????? ????? StringBuffer? StringBuilder?? ????.

?: StringBuffer? ??? ???

?? ??? ???? ???? StringBuffer? ?????.

public class StringBufferBasics {

    public void threadSafe() {
        // Common resource being shared
        StringBuffer buffer = new StringBuffer();

        // Thread appending "A" 1000 times
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                buffer.append("A");
            }
        });

        // Thread appending "B" 1000 times
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                buffer.append("B");
            }
        });

        t1.start();
        t2.start();

        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // Result: 2000
        System.out.println("Length: " + buffer.toString().length());
    }

    public static void main(String[] args) {
        new StringBufferBasics().threadSafe();
    }
}

??:

• StringBuffer? ? ???? ?? ???? ???? ?? ??? 2000? ????? ?????.

• ?? ???? ?????? ????? ??? ?? ??? ????????(?: "AAABBB..." ??)? ? ????. ??>.

??: ??? ???? ???? ???? ??? ????? ???????? StringBuffer? ?????.

• ??? ???? ??? ???? ??? ?? ?? ?? ??? ??????? StringBuilder? ?????.

• ?? ??? ??? ??? ???? ?? ??? ??? ?? ??? ???? ??? ?? ??? ?????? StringBuffer? ?????.

??

? ??? StringBuilder? StringBuffer ???? ??? ???? ???? ? ??? ???. ???, ?? ? ??? ???? ???? ???? Java?? ???? ??? ? ? ?? ?? ??? ?? ? ????.

?? ???

• ?? ??
• ??? ??? ????
• Java ??? ?? ??
• Java ??? ??
• Java OOP ??
• ?? ????? ??

??? ?????!

? ??? Java? StringBuilder ? StringBuffer? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!