import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;
public class StringBuilderAndBufferTest implements Runnable{ static StringBuilder builder = new StringBuilder(); static StringBuffer buffer=new StringBuffer();
public void run() { try { Thread.sleep((int)(Math.random() * 2)); } catch (InterruptedException e) { e.PRintStackTrace(); } builder.append("1"); buffer.append("1");}public static void main(String[] args) throws InterruptedException { ExecutorService pool = Executors.newFixedThreadPool(50); for (int i = 0; i < 30000; i++) { pool.execute(new StringBuilderAndBufferTest()); } Thread.sleep(3000); // 如果長度為30000就是安全的 System.out.println("StringBuilder長度==="+builder.length()); System.out.println("StringBuffer長度==="+buffer.length());}}
結(jié)果如下：
StringBuilder長度===29536StringBuffer長度===30000
查看二者append()方法的區(qū)別
public StringBuilder append(String str) { super.append(str); return this;}public synchronized StringBuffer append(String str) { super.append(str); return this;}public AbstractStringBuilder append(String str) { if (str == null) str = "null"; int len = str.length(); ensureCapacityInternal(count + len); str.getChars(0, len, value, count); count += len; return this;}二者底層都是調(diào)用父類AbstractStringBuilder的append(String str)，區(qū)別在于StringBuffer的append方法有synchronized關(guān)鍵字。synchronized關(guān)鍵字表示該方法一次只能有一個(gè)線程進(jìn)入，其他線程要想在此時(shí)調(diào)用該方法,只能排隊(duì)等候,當(dāng)前線程(就是在synchronized方法內(nèi)部的線程)執(zhí)行完該方法后,別的線程才能進(jìn)入
故可知：
StringBuilder是非線程安全的，效率更高；
StringBuffer是線程安全的，效率不如StringBuilder。
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