級聯

Java 語法

等級 3 , 課堂 5

開放

“我想告訴你如何合併字符串。合併或連接字符串的過程通常使用簡稱“連接”來表示。貓愛好者會發現它很容易記住：con-Cat-en-Nation。我開玩笑的。

“合併字符串的規則很簡單。如果我們‘添加’(+) 一個字符串和其他東西，那麼‘其他’會通過 toString() 方法隱式轉換為字符串。 ”

“你剛才是在跟我說話嗎？”

“好吧，我會用更簡單的方式解釋它。如果我們添加一個字符串，一個數字和一隻貓，那麼數字和貓都會被轉換為字符串。這裡有一些例子：”

代碼	等效代碼
`Cat cat = new Cat(); String text = "The cat is " + cat;`	`Cat cat = new Cat();` `String s = cat.toString();` `String text = "The cat is " + s;`
`int a = 5; String text = "a is " + a;`	`int a = 5;` `String s = Integer.toString(a);` `String text = "a is " + s;`
`int a = 5; String text = a + "a is ";`	`int a = 5;` `String s = Integer.toString(a);` `String text = s + "a is ";`
`Cat cat = new Cat(); int a = 5; String text = "The cat is " + cat + a;`	`Cat cat = new Cat();` `String s1 = cat.toString();` `String s2 = Integer.toString(a);` `String text = "The cat is " + s1 + s2;`
`Cat cat = new Cat(); int a = 5; String text = a + "The cat is " + cat + a;`	`Cat cat = new Cat();` `String s1 = cat.toString();` `String s2 = Integer.toString(a);` `String s3 = Integer.toString(a);` `String text = s3 + "The cat is " + s1 + s2;`
`Cat cat = new Cat(); int a = 5; String text = cat + a + "The cat is " + cat + a;`	該程序將無法編譯！加法運算是從左到右執行的，所以我們得到：如果我們給一個數字加上一隻貓，沒有自動的字符串轉換。 `String text = (((cat + a) + "The cat is ") + cat) + a;`
`// But you can do this: Cat cat = new Cat(); int a = 5; String text = cat + (a + "The cat is ") + cat + a; // This is the same as: Cat cat = new Cat(); int a = 5; String text = ((cat + (a + "The cat is ")) + cat)+a;`	`Cat cat = new Cat();` `String s1 = cat.toString();` `String s2 = cat.toString();` `String s3 = Integer.toString(a);` `String s4 = Integer.toString(a);` `String text = s1 + s3 + "The cat is " + s2 + s4;`