什么是 java String compareTo 方法和什么是字典顺序的 Java

Question

不知道输出是什么意思？有人会帮我吗？请解释一下它是如何工作的。

  public class LastIndexOfExample{  
  public static void main(String args[]){  
   String s1="hello";  
   String s2="hello";  
   String s3="meklo";  
   String s4="hemlo";  
   System.out.println(s1.compareTo(s2));  
   System.out.println(s1.compareTo(s3));  
   System.out.println(s1.compareTo(s4));  
  }
}

那么输出是： 0 -5 -1

Answer 1

来自 compareTo javadoc:

If there is an index at which the two strings differ, the result is the difference between the two char's at the lowest such index

完整的 Javadoc：

    /**
     * Compares this string to the given string.
     *
     * <p>The strings are compared one {@code char} at a time.
     * In the discussion of the return value below, note that {@code char} does not
     * mean code point, though this should only be visible for surrogate pairs.
     *
     * <p>If there is an index at which the two strings differ, the result is
     * the difference between the two {@code char}s at the lowest such index.
     * If not, but the lengths of the strings differ, the result is the difference
     * between the two strings' lengths.
     * If the strings are the same length and every {@code char} is the same, the result is 0.
     *
     * @throws NullPointerException
     *             if {@code string} is {@code null}.
     */
    public native int compareTo(String string);

并来自联机文档（link 以上）：

The result is a negative integer if this String object lexicographically precedes the argument string

什么是 java String compareTo 方法和什么是字典顺序的 Java

What is java String compareTo method and What is Java lexicographically

java

string-comparison