深入了解java中的逃逸分析

public static StringBuffer craeteStringBuffer(String s1, String s2) {
  StringBuffer sb = new StringBuffer();
  sb.append(s1);
  sb.append(s2);
  return sb;
}

public static String createStringBuffer(String s1, String s2) {
  StringBuffer sb = new StringBuffer();
  sb.append(s1);
  sb.append(s2);
  return sb.toString();
}

public void f() {
  Object o = new Object();
  synchronized(o) {
    System.out.println(o);
  }
}

public void f() {
  Object o = new Object();
  System.out.println(o);
}

public static void main(String[] args) {
  alloc();
}

private static void alloc() {
  Point point = new Point（1,2）;
  System.out.println("point.x="+point.x+"; point.y="+point.y);
}
class Point{
  private int x;
  private int y;
}

private static void alloc() {
  int x = 1;
  int y = 2;
  System.out.println("point.x="+x+"; point.y="+y);
}

public static void main(String[] args) {
  long a1 = System.currentTimeMillis();
  for (int i = 0; i < 1000000; i++) {
    alloc();
  }
  // 查看执行时间
  long a2 = System.currentTimeMillis();
  System.out.println("cost " + (a2 - a1) + " ms");
  // 为了方便查看堆内存中对象个数，线程sleep
  try {
    Thread.sleep(100000);
  } catch (InterruptedException e1) {
    e1.printStackTrace();
  }
}

private static void alloc() {
  User user = new User();
}

static class User {

}

Xmx4G -Xms4G -XX:-DoEscapeAnalysis -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError

➜ ~ jps
2809 StackAllocTest
2810 Jps
➜ ~ jmap -histo 2809

 num   #instances     #bytes class name
----------------------------------------------
  1:      524    87282184 [I
  2:    1000000    16000000 StackAllocTest$User
  3:     6806    2093136 [B
  4:     8006    1320872 [C
  5:     4188     100512 java.lang.String
  6:      581     66304 java.lang.Class

-Xmx4G -Xms4G -XX:+DoEscapeAnalysis -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError 

➜ ~ jps
709
2858 Launcher
2859 StackAllocTest
2860 Jps
➜ ~ jmap -histo 2859

 num   #instances     #bytes class name
----------------------------------------------
  1:      524   101944280 [I
  2:     6806    2093136 [B
  3:     83619    1337904 StackAllocTest$User
  4:     8006    1320872 [C
  5:     4188     100512 java.lang.String
  6:      581     66304 java.lang.Class