String,StringBuffer,StringBuilder的区别

public static void main(String[] args) {
    String str = new String("hello....");
    StringBuffer stringBuffer = new StringBuffer(str);
    StringBuilder stringBuilder = new StringBuilder();
    
    stringBuffer.append("world").append("!!");
    //System.out.println(stringBuffer.reverse());//字符串反转
    stringBuffer.insert(7, "$$");
    System.out.println(stringBuffer.toString());
    //stringBuffer.delete(start, end)
    
    /**
     * String,StringBuffer,StringBuilder的区别：
     * String类的内容一旦声明则不可改变，StringBuffer,StringBuilder的内容可以改变
     * 三者都是CharSequence接口的子类
     * StringBuffer是从JDK1.0时提供的，属于线程安全的操作，是同步操作，因为方法上有synchronized关键字
     * StringBuilder是从JDK1.5出现的，线程不安全，是异步操作，但效率高
     * 多线程访问同一资源时，必须用StringBuffer
     *
     **/
}

public final class StringBuffer
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence

StringBuffer 的 append()

@Override
    public synchronized StringBuffer append(String str) {
        toStringCache = null;
        super.append(str);
        return this;
    }

public final class StringBuilder
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence

StringBuilder 的 append()

@Override
    public StringBuilder append(String str) {
        super.append(str);
        return this;
    }