Comparison of string and stringbuffer Efficiency

Let's take a look at the connection between two simple strings.Code

 

1 Public Class Test {
2 Public Static String testjoinstring (){
3 String STR = "A" + "";
4 Return STR;
5 }
6
7 Public Static String testjomongoingbuffer (){
8 Stringbuffer sb = New Stringbuffer ();
9 SB. append ("");
10 SB. append ("");
11 Return SB. tostring ();
12 }
13 }

 

After compilation

Javap-verbose test> test.txtDecompile bytecodeJavaIntermediate code. Directly look at the subject.

 

--------------------------------------------

Public static java. Lang. String testjoinstring ();

Code:

Stack = 1, locals = 1, args_size = 0

0: LDC #16; // string AA

2: astore_0

3: aload_0

4: areturn

 

Public static java. Lang. String testjoinstringbuffer ();

Code:

Stack = 2, locals = 1, args_size = 0

0: New #21; // class Java/lang/stringbuffer

3: DUP

4: invokespecial #23; // method Java/lang/stringbuffer. "<init>" :() V

7: astore_0

8: aload_0

9: LDC #24; // string

11: invokevirtual #26; // method Java/lang/stringbuffer. append :( ljava/lang/string;) ljava/lang/stringbuffer;

14: Pop

15: aload_0

16: LDC #24; // string

18: invokevirtual #26; // method Java/lang/stringbuffer. append :( ljava/lang/string;) ljava/lang/stringbuffer;

21: Pop

22: aload_0

23: invokevirtual #30; // method Java/lang/stringbuffer. tostring :() ljava/lang/string;

26: areturn

--------------------------------------------

 

Look at the red part

StringConnection:

0: LDC #16; // string AA,

We can see that during compilation, expressions have been directly merged and optimized, So we loaded them directly.AA

StringbufferIn the case:

9: LDC #24; // string

16: LDC #24; // string

Loaded twice

 

From the above we can see that in the case of a few simple strings and strings that do not involve variables. The string + number connection has been optimized during compilation, so the efficiency is higher than that of stringbuffer.

 

Next let's take a look at how simple strings are connected to variables.

1 Public Class Test1 {
2 Public Static String testjoinstring (){
3 String str1 = "";
4 String str2 = "A" + str1;
5 Return Str2;
6 }
7 Public Static String testjomongoingbuffer (){
8 Stringbuffer sb = New Stringbuffer ();
9 SB. append ("");
10 SB. append ("");
11 Return SB. tostring ();
12 }
13 }

 

 

Similarly, in cmdJavap-verbose test1> test1.txt

View subject

 

--------------------------------------------

Public static java. Lang. String testjoinstring ();

Code:

Stack = 3, locals = 2, args_size = 0

0: LDC #16; // string

2: astore_0

3: New #18; // class Java/lang/stringbuilder

6: DUP

7: LDC #16; // string

9: invokespecial #20; // method Java/lang/stringbuilder. "<init>" :( ljava/lang/string;) V

12: aload_0

13: invokevirtual #23; // method Java/lang/stringbuilder. append :( ljava/lang/string;) ljava/lang/stringbuilder;

16: invokevirtual #27; // method Java/lang/stringbuilder. tostring :() ljava/lang/string;

19: astore_1

20: aload_1

21: areturn

--------------------------------------------

 

StringbufferSome code is not changed to space saving. It is not listed here. You can take a look at it.

 

Check the red part again.

StringOf+Number connection

0: LDC #16; // string

7: LDC #16; // string

13: invokevirtual #23;

// Method Java/lang/stringbuilder. append :( ljava/lang/string;) ljava/lang/stringbuilder;

We can see thatStringOf+Number connection, still calledStringbuffer. appendMethod.

 

Therefore, when a few simple strings are connected to variables, the efficiency of the two is basically the same.

 

 

Next let's look at the last situation. Code connecting a large number of strings and variables

 

1 Public Class Test2 {
2 Public Static String testjoinstring (){
3 String STR = "";
4 For ( Int I = 0; I <100; I ++ ){
5 STR + = "A" + I;
6 }
7 Return STR;
8 }
9
10 Public Static String testjomongoingbuffer (){
11 Stringbuffer sb = New Stringbuffer ();
12 For ( Int I = 0; I <100; I ++ ){
13 SB. append ("");
14 SB. append (I );
15 }
16 Return SB. tostring ();
17 }
18 }

 

 

Javap-verbose Test2> test2.txt

Subject

--------------------------------------------

Public static java. Lang. String testjoinstring ();

Code:

Stack = 3, locals = 2, args_size = 0

0: LDC #16; // string

2: astore_0

3: iconst_0

4: istore_1

5: goto 35

8: New #18; // class Java/lang/stringbuilder

11: DUP

12: aload_0

13: invokestatic #20;

// Method Java/lang/string. valueof :( ljava/lang/object;) ljava/lang/string;

16: invokespecial #26; // method Java/lang/stringbuilder. "<init>" :( ljava/lang/string;) V

19: LDC #16; // string

21: invokevirtual #29;

// Method Java/lang/stringbuilder. append :( ljava/lang/string;) ljava/lang/stringbuilder;

24: iload_1

25: invokevirtual #33;

// Method Java/lang/stringbuilder. append :( I) ljava/lang/stringbuilder;

28: invokevirtual #36; // method Java/lang/stringbuilder. tostring :() ljava/lang/string;

31: astore_0

32: iinc 1, 1

35: iload_1

36: bipush 100

38: if_icmplt 8

41: aload_0

42: areturn

 

Public static java. Lang. String testjoinstringbuffer ();

Code:

Stack = 2, locals = 2, args_size = 0

0: New #45; // class Java/lang/stringbuffer

3: DUP

4: invokespecial #47; // method Java/lang/stringbuffer. "<init>" :() V

7: astore_0

8: iconst_0

9: istore_1

10: goto 29

13: aload_0

14: LDC #16; // string

16: invokevirtual #48;

// Method Java/lang/stringbuffer. append :( ljava/lang/string;) ljava/lang/stringbuffer;

19: Pop

20: aload_0

21: iload_1

22: invokevirtual #51; // method Java/lang/stringbuffer. append :( I) ljava/lang/stringbuffer;

25: Pop

26: iinc 1, 1

29: iload_1

30: bipush 100

32: if_icmplt 13

35: aload_0

36: invokevirtual #54; // method Java/lang/stringbuffer. tostring :() ljava/lang/string;

39: areturn

------------------------------------------

 

Look at the red part above.(Subject)

Testjoinstring

5: goto 35

8: New #18; // class Java/lang/stringbuilder

19: LDC #16; // string

21: invokevirtual #29;

// Method Java/lang/stringbuilder. append :( ljava/lang/string;) ljava/lang/stringbuilder;

25: invokevirtual #33;

// Method Java/lang/stringbuilder. append :( I) ljava/lang/stringbuilder;

28: invokevirtual #36; // method Java/lang/stringbuilder. tostring :() ljava/lang/string;

36: bipush 100

38: if_icmplt 8

 

Testjoinstringbuffer

0: New #45; // class Java/lang/stringbuffer

13: aload_0

14: LDC #16; // string

16: invokevirtual #48;

// Method Java/lang/stringbuffer. append :( ljava/lang/string;) ljava/lang/stringbuffer;

22: invokevirtual #51; // method Java/lang/stringbuffer. append :( I) ljava/lang/stringbuffer;

30: bipush 100

32: if_icmplt 13

 

We can see from the above. String Of + Number connection , Inside the loop body (8 ~ 28) , Every time New One Stringbuffer Come out, and Stringbuffer. append Method, only in vitro, New One Stringbuffer .

In this case, if the cycle is large,StringOf+Number connection is quite resource-consuming and time-consuming.

 

Therefore, in the case of a large number of connections.StringbufferThe efficiency is significantly higherStringOf+Connection