java - What does the following method call statement mean in Java?

Question

    StringBuilder str = new StringBuilder("Today");
    str.append(" is ").append("a").append(" sunny ").append(" day.");

In the java code above, I understand that first I created an object of type StringBuilder. Then I used the object reference str to access the method append of the class StringBuilder. After this, I loose track. Is the method append used after str.append("is") inside the append method, or am I calling the same method in this class? Further, can anyone explain the flow of execution of the above statement. Which of the above append methods is executed first?

Answer 1

方法的返回值append是StringBuilder对象本身。因此，您可以链接调用并向字符串添加更多字符。否则，代码将很难阅读，因为您必须每行都引用 StringBuilder 对象。

Answer 2

str.append(" is ")返回 StringBuilder 本身。您正在对该方法返回的对象调用方法。这和做的一样

user.getAddress().getStreet().charAt(0);

除了在您的代码中，每个append()方法调用都返回相同的对象，这允许将多个方法调用链接到同一个 StringBuilder。

Answer 3

考虑看看Builder Pattern（向下滚动到页面末尾）。基本上，对象总是返回自己，因此您可以链接许多命令。

Answer 4

StringBuilder str = new StringBuilder("Today");
str.append(" is ").append("a").append(" sunny ").append(" day.");

这里str.append(" is ")返回StringBuilder您再次调用 append("a")methnod 的对象。

str.append(" is ").append("a")再次返回StringBuilder参考，再次调用append(" sunny ")方法等等。

所以基本上你正在链接方法，就是这样。