optimizations when translating java source code to bytecode

Are there any optimiza开发者_运维技巧tions, such as dead code elimination, involved when translating java source files to bytecodes?

The standard Java compilers do few optimizations on the emitted bytecodes. I think that the reasoning is that unoptimized bytecodes will be easier for the HotSpot JIT compiler to optimize.

The links that @Mitch Wheat provided in comments above (particularly the 2nd one) date from the days when HotSpot JIT was new technology.

While searching all source code optimization, i came across this question and though I am answering after long time this question asked.

After jdk1.7, String concatenation using plus [+] operator converted to StringBuilder append e.g

public static void main(String[] args) {
String s = new String("");
s = s+"new";
}

Converted to StringBuilder append as shown in bytecode

public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=2, args_size=1
         0: new           #2                  // class java/lang/String
         3: dup
         4: ldc           #3                  // String
         6: invokespecial #4                  // Method java/lang/String."<init>":(Ljava/lang/String;)V
         9: astore_1
        10: new           #5                  // class java/lang/StringBuilder
        13: dup
        14: invokespecial #6                  // Method java/lang/StringBuilder."<init>":()V
        17: aload_1
        18: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        21: ldc           #8                  // String new
        23: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        26: invokevirtual #9                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
        29: astore_1
        30: return
      LineNumberTable:
        line 13: 0
        line 14: 10
        line 15: 30
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      31     0  args   [Ljava/lang/String;
           10      21     1     s   Ljava/lang/String;
}