[Effective Java] Rule 51. Use StringBuilder when you add strings

Compiled Bytecode.txt

λ javac StringConcat.java
λ javap -c StringConcat.class
Picked up JAVA_TOOL_OPTIONS: -Xmx8g
Compiled from "StringConcat.java"
public class StringConcat {
  public StringConcat();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: ldc           #2                  // String
       2: astore_1
       3: iconst_0
       4: istore_2
       5: iload_2
       6: aload_0
       7: arraylength
       8: if_icmpge     43
      11: new           #3                  // class java/lang/StringBuilder
      14: dup
      15: invokespecial #4                  // Method java/lang/StringBuilder."<init>":()V
      18: aload_1
      19: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      22: aload_0
      23: iload_2
      24: aaload
      25: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      28: ldc           #6                  // String ,
      30: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      33: invokevirtual #7                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      36: astore_1
      37: iinc          2, 1
      40: goto          5
      43: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
      46: aload_1
      47: invokevirtual #9                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      50: new           #3                  // class java/lang/StringBuilder
      53: dup
      54: invokespecial #4                  // Method java/lang/StringBuilder."<init>":()V
      57: astore_2
      58: iconst_0
      59: istore_3
      60: iload_3
      61: aload_0
      62: arraylength
      63: if_icmpge     87
      66: aload_2
      67: aload_0
      68: iload_3
      69: aaload
      70: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      73: pop
      74: aload_2
      75: ldc           #6                  // String ,
      77: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      80: pop
      81: iinc          3, 1
      84: goto          60
      87: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
      90: aload_2
      91: invokevirtual #10                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      94: return
}

StringConcat.java

public class StringConcat {
  public static void main(String[] args) {
    String result = "";
    for(int i=0; i<args.length; ++i) {
      result += args[i] + ",";
    }
    System.out.println(result);

    StringBuilder result2 = new StringBuilder();
    for(int j=0; j<args.length; ++j) {
      result2.append(args[j]);
      result2.append(",");
    }
    System.out.println(result2);
  }
}