Java toString() 方法

Question

public String toString()
        {
        String str;
        str = "The test scores in descending order are \n";

        for(int i = 0; i < data.length; i++)
        {
            str = str + data[i] + " ";
        }
        str = str + "\nThe average is " + mean;
        return str;
        }

此 java 代码按我的代码的降序返回分数。但让我失望的是返回“str”的方式。我的理解是 'str' 的返回值是 (str + "\nThe average is "+ mean)。因为这是我最后更新的'str'值，它会将'str'更新为“The test scores in descending order are” First, Second the loop, then last "str + "\nThe average is "+ mean".所以最后即使我们更新了 str 几次，实际打印的 'str' 也只会是 "str + "\n平均值是 "+ mean"。请解释为什么程序最终打印出来了

考试成绩从高到低依次为 70 80 ..........(元素值)

(然后返回平均值信息)

Answer 1

因为命令是

str = str + "\nThe average is " + mean;

这意味着，附加到 str 中的所有内容并将结果存储在 str 中。如果是

str = "\nThe average is " + mean;

它会替换 str 中已有的所有内容。