字符串相等(==)的全测试

最新推荐文章于 2022-10-11 07:58:30 发布

最新推荐文章于 2022-10-11 07:58:30 发布 · 161 阅读

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本文详细解析了Java中字符串比较的六种情况，包括相同包内相同及不同类间的字符串常量比较、运行时计算字符串的比较，以及字符串常量化的使用。

 package p1;
/**
 * 字符串相等(==)的全测试。
 * 
 * @author XT Zang,老紫竹
 */
class TestString1 {
  public static void main(String[] args) {
    String hello = "Hello", lo = "lo";
    System.out.print((hello == "Hello") + " "); // true
    System.out.print((Other.hello == hello) + " "); // true
    System.out.print((p2.Other.hello == hello) + " "); // true
    System.out.print((hello == ("Hel" + "lo")) + " "); // true
    System.out.print((hello == ("Hel" + lo)) + " "); // false
    System.out.println(hello == ("Hel" + lo).intern()); // true
  }
}
class Other {
  static String hello = "Hello";
}

 package p2;
public class Other {
  public static String hello = "Hello";
}

结论：

This example illustrates six points:

Literal strings within the same class (§8) in the same package (§7) represent references to the same String object (§4.3.1).相同包，相同类的字符串常量指向相同的字符串对象
Literal strings within different classes in the same package represent references to the same String object.相同包，不相同类的字符串常量指向相同的字符串对象
Literal strings within different classes in different packages likewise represent references to the same String object.不同包，不同类的字符串常量指向相同的字符串对象
Strings computed by constant expressions (§15.28) are computed at compile time and then treated as if they were literals.字符串在编译期间可以连接起来的，视同一个常量字符串
Strings computed by concatenation at run time are newly created and therefore distinct.