java - Which code snippet executes faster? -
i can same thing 2 types of code snippet.
first way:
string makedate = integer.tostring(now.year) + integer.tostring(now.month) + integer.tostring(now.monthday); or second way:
string makedate = now.year + "" + now.month + "" + now.monthday; my question is:
- which method preferable [first way or second way]?
- which code snippet execute faster?
the 2 snippits show identical.
a string in java immutable; can't changed. when using concatenation operator (+) compiler generates code using stringbuilder
for example second snippit becomes:
string makedate = new stringbuilder() .append(now.year) .append("") .append(now.month) .append("") .append(now.monthday) .tostring(); you can @ generated bytecode see this. java comes program javap allows @ compiled .class.
i created simple main() provide minimal bytecode:
public static void main(string[] args) { string makedate = integer.tostring(1) + integer.tostring(1) + integer.tostring(1); system.out.println(makedate); } which produces:
public static void main(java.lang.string[]); flags: acc_public, acc_static code: stack=2, locals=2, args_size=1 0: new #2 // class java/lang/stringbuilder 3: dup 4: invokespecial #3 // method java/lang/stringbuilder."<init>":()v 7: iconst_1 8: invokestatic #4 // method java/lang/integer.tostring:(i)ljava/lang/string; 11: invokevirtual #5 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 14: iconst_1 15: invokestatic #4 // method java/lang/integer.tostring:(i)ljava/lang/string; 18: invokevirtual #5 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 21: iconst_1 22: invokestatic #4 // method java/lang/integer.tostring:(i)ljava/lang/string; 25: invokevirtual #5 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 28: invokevirtual #6 // method java/lang/stringbuilder.tostring:()ljava/lang/string; 31: astore_1 32: getstatic #7 // field java/lang/system.out:ljava/io/printstream; 35: aload_1 36: invokevirtual #8 // method java/io/printstream.println:(ljava/lang/string;)v 39: return versus:
public static void main(string[] args) { int = 1; string makedate = + "" + + "" + i; system.out.println(makedate); } produces:
public static void main(java.lang.string[]); flags: acc_public, acc_static code: stack=2, locals=3, args_size=1 0: iconst_1 1: istore_1 2: new #2 // class java/lang/stringbuilder 5: dup 6: invokespecial #3 // method java/lang/stringbuilder."<init>":()v 9: iload_1 10: invokevirtual #4 // method java/lang/stringbuilder.append:(i)ljava/lang/stringbuilder; 13: ldc #5 // string 15: invokevirtual #6 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 18: iload_1 19: invokevirtual #4 // method java/lang/stringbuilder.append:(i)ljava/lang/stringbuilder; 22: ldc #5 // string 24: invokevirtual #6 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 27: iload_1 28: invokevirtual #4 // method java/lang/stringbuilder.append:(i)ljava/lang/stringbuilder; 31: invokevirtual #7 // method java/lang/stringbuilder.tostring:()ljava/lang/string; 34: astore_2 35: getstatic #8 // field java/lang/system.out:ljava/io/printstream; 38: aload_2 39: invokevirtual #9 // method java/io/printstream.println:(ljava/lang/string;)v 42: return technically latter faster @ scale immeasurable (< 1ns) practical purposes doesn't matter; use whichever like.
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