String字符串性能优化的几种方案

publicclasstest3 {
publicstaticvoidmain(String[] args) {
Stringstr="ab"+"cd"+"ef"+"123";
     }
 }

// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.// Jad home page: http://www.kpdus.com/jad.html// Decompiler options: packimports(3) annotate // Source File Name:   test.javapackageexample;
publicclasstest  {
publictest()
      {
//    0    0:aload_0         //    1    1:invokespecial   #1   <Method void Object()>//    2    4:return               }
publicstaticvoidmain(Stringargs[])
     {
Stringstr="abcdef123";
//    0    0:ldc1            #2   <String "abcdef123">//    1    2:astore_1        //    2    3:return               }
 }

publicclasstest1 {
publicstaticvoidmain(String[] args)
     {
Strings="abc";
Stringss="ok"+s+"xyz"+5;
System.out.println(ss);
     }
 }

// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.// Jad home page: http://www.kpdus.com/jad.html// Decompiler options: packimports(3) annotate // Source File Name:   test1.javapackageexample;
importjava.io.PrintStream;
publicclasstest1 {
publictest1()
     {
//    0    0:aload_0         //    1    1:invokespecial   #1   <Method void Object()>//    2    4:return               }
publicstaticvoidmain(Stringargs[])
     {
Strings="abc";
//    0    0:ldc1            #2   <String "abc">//    1    2:astore_1        Stringss= (newStringBuilder()).append("ok").append(s).append("xyz").append(5).toString();
//    2    3:new             #3   <Class StringBuilder>//    3    6:dup             //    4    7:invokespecial   #4   <Method void StringBuilder()>//    5   10:ldc1            #5   <String "ok">//    6   12:invokevirtual   #6   <Method StringBuilder StringBuilder.append(String)>//    7   15:aload_1         //    8   16:invokevirtual   #6   <Method StringBuilder StringBuilder.append(String)>//    9   19:ldc1            #7   <String "xyz">//   10   21:invokevirtual   #6   <Method StringBuilder StringBuilder.append(String)>//   11   24:iconst_5        //   12   25:invokevirtual   #8   <Method StringBuilder StringBuilder.append(int)>//   13   28:invokevirtual   #9   <Method String StringBuilder.toString()>//   14   31:astore_2        System.out.println(ss);
//   15   32:getstatic       #10  <Field PrintStream System.out>//   16   35:aload_2         //   17   36:invokevirtual   #11  <Method void PrintStream.println(String)>//   18   39:return               }
 }

publicclasstest2 {
publicstaticvoidmain(String[] args) {
Strings="";
Randomrand=newRandom();
for (inti=0; i<10; i++) {
s=s+rand.nextInt(1000) +" ";
          }
System.out.println(s);
      }
 }

// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.// Jad home page: http://www.kpdus.com/jad.html// Decompiler options: packimports(3) annotate // Source File Name:   test2.javapackageexample;
importjava.io.PrintStream;
importjava.util.Random;
publicclasstest2  {
publictest2()
     {
//    0    0:aload_0         //    1    1:invokespecial   #1   <Method void Object()>//    2    4:return               }
publicstaticvoidmain(Stringargs[])
     {
Strings="";
//    0    0:ldc1            #2   <String "">//    1    2:astore_1        Randomrand=newRandom();
//    2    3:new             #3   <Class Random>//    3    6:dup             //    4    7:invokespecial   #4   <Method void Random()>//    5   10:astore_2        for(inti=0; i<10; i++)
//*   6   11:iconst_0        //*   7   12:istore_3        //*   8   13:iload_3         //*   9   14:bipush          10//*  10   16:icmpge          55s= (newStringBuilder()).append(s).append(rand.nextInt(1000)).append(" ").toString();
//   11   19:new             #5   <Class StringBuilder>//   12   22:dup             //   13   23:invokespecial   #6   <Method void StringBuilder()>//   14   26:aload_1         //   15   27:invokevirtual   #7   <Method StringBuilder StringBuilder.append(String)>//   16   30:aload_2         //   17   31:sipush          1000//   18   34:invokevirtual   #8   <Method int Random.nextInt(int)>//   19   37:invokevirtual   #9   <Method StringBuilder StringBuilder.append(int)>//   20   40:ldc1            #10  <String " ">//   21   42:invokevirtual   #7   <Method StringBuilder StringBuilder.append(String)>//   22   45:invokevirtual   #11  <Method String StringBuilder.toString()>//   23   48:astore_1        //   24   49:iinc            3  1//*  25   52:goto            13System.out.println(s);
//   26   55:getstatic       #12  <Field PrintStream System.out>//   27   58:aload_1         //   28   59:invokevirtual   #13  <Method void PrintStream.println(String)>//   29   62:return               }
 }

publicclasstest4 {
publicstaticvoidmain(String[] args) {
finalintMAX=10000000;
System.out.println("不用intern："+notIntern(MAX));
//      System.out.println("使用intern："+intern(MAX));      }
privatestaticlongnotIntern(intMAX){
longstart=System.currentTimeMillis();
for (inti=0; i<MAX; i++) {
intj=i%100;
Stringstr=String.valueOf(j);
         }
returnSystem.currentTimeMillis() -start;
     }
/*private static long intern(int MAX){long start = System.currentTimeMillis();for (int i = 0; i < MAX; i++) {int j = i % 100;String str = String.valueOf(j).intern();}return System.currentTimeMillis() - start;}*/

publicclasstest5 {
publicstaticvoidmain(String[] args) {
Strings1=newString("ab");
s.intern();
Strings2="ab";
System.out.println(s1==s2);
Strings3=newString("ab")+newString("cd");
s3.intern();
Strings4="abcd";
System.out.println(s4==s3);
     }
 }