@Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("{stack=");
        builder.append(Arrays.toString(stack));
        builder.append(", index=");
        builder.append(index);
        builder.append(", factory=");
        builder.append(factory);
        builder.append("}");
        return builder.toString();
    }
@author netspider
@author Woonduk Kang(emeroad)
@author jaehong.kim
agent-module/profiler/src/main/java/com/navercorp/pinpoint/profiler/context/DefaultCallStack.java