我正在讨论如何在
Java中使用Strings和StringBuffers.在这两个例子的每一个中创建了多少个对象？
例1：
- String s = "a";
- s = s + "b";
- s = s + "c";
例2：
- StringBuilder sb = new StringBuilder("a");
- sb.append("b");
- sb.append("c");
在我看来,Ex 1将创建5,而Ex 2将创建4个对象.
解决方法
您可以通过分析java字节码来确定答案(使用javap -c).示例1创建了两个StringBuilder对象(参见第4行)和两个String对象(参见第7行),而示例2创建了一个StringBuilder对象(参见第2行).
请注意,您还必须考虑char []对象(因为数组是Java中的对象). String和StringBuilder对象都使用底层char []实现.因此,示例1创建了八个对象,示例2创建了两个对象.
例1：
- public static void main(java.lang.String[]);
- Code:
- 0: ldc #2; //String a
- 2: astore_1
- 3: new #3; //class java/lang/StringBuilder
- 6: dup
- 7: invokespecial #4; //Method java/lang/StringBuilder."<init>":()V
- 10: aload_1
- 11: invokevirtual #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 14: ldc #6; //String b
- 16: invokevirtual #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 19: invokevirtual #7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
- 22: astore_1
- 23: new #3; //class java/lang/StringBuilder
- 26: dup
- 27: invokespecial #4; //Method java/lang/StringBuilder."<init>":()V
- 30: aload_1
- 31: invokevirtual #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 34: ldc #8; //String c
- 36: invokevirtual #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 39: invokevirtual #7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
- 42: astore_1
- 43: return
- }
例2：
- public static void main(java.lang.String[]);
- Code:
- 0: new #2; //class java/lang/StringBuilder
- 3: dup
- 4: ldc #3; //String a
- 6: invokespecial #4; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
- 9: astore_1
- 10: aload_1
- 11: ldc #5; //String b
- 13: invokevirtual #6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 16: pop
- 17: aload_1
- 18: ldc #7; //String c
- 20: invokevirtual #6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
- 23: pop
- 24: return
- }
