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@bwmcadams
Last active August 29, 2015 14:25
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Java String Concatenation Performance
// decompiled with straight javap -c
//Compiled from "TestStrings.java" in JAVA 1.6.... same in newer versions.
public class TestStrings extends java.lang.Object{
public TestStrings();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
// Note that "Foo " + "bar" was replaced (by compiler) with a static string of "Foo bar"
0: ldc #2; //String Foo bar
2: astore_1
// Note that "OMG" + "WTF" + "BBQ" was replaced (by compiler) with a static string of "OMGWTFBBQ"
3: ldc #3; //String OMGWTFBBQ
5: astore_2
// String variable 'foo' + String variable 'omg' is compiler substituted with a StringBuilder construction...
6: new #4; //class java/lang/StringBuilder
9: dup
10: invokespecial #5; //Method java/lang/StringBuilder."<init>":()V
13: aload_1
14: invokevirtual #6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
17: aload_2
18: invokevirtual #6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
21: invokevirtual #7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
24: astore_3
25: return
}
public class TestStrings {
public static void main(String[] args) {
String foo = "Foo " + "bar";
String omg = "OMG" + "WTF" + "BBQ";
String test = foo + omg;
}
}
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