有兩個方法可以得到物件的型別
- instanceof，除了可以得到物件的型別，也可以得到物件的繼承關係。
- getClass搭配equals，只能判斷物件與類別的直接關係，不能判斷物件的繼承關係。
可以參考下方例子會更清楚。
Cat類別繼承Animal類別，而Airplane實作Flyer介面
public class Test {
public static void main(String[] args) {
Cat cat = new Cat();
Airplane airplane = new Airplane();
// instanceof
if (cat instanceof Animal) {
System.out.println("cat is Animal class");
}
if (cat instanceof Cat) {
System.out.println("cat is Cat class");
}
System.out.println("========================");
// getClass
if (cat.getClass().equals(Animal.class)) {
System.out.println("cat is Animal class");
}
if (cat.getClass().equals(Cat.class)) {
System.out.println("cat is Cat class");
}
System.out.println("========================");
if (cat.getClass().equals(Airplane.class)) {
System.out.println("cat is Dog class");
} else {
System.out.println("cat is not Dog class");
}
System.out.println("========================");
if (airplane instanceof Airplane) {
System.out.println("airplane is Airplane class");
}
if (airplane instanceof Flyer) {
System.out.println("airplane is Flyer class");
}
System.out.println("========================");
if (airplane.getClass().equals(Airplane.class)) {
System.out.println("airplane is Airplane class");
}
if (airplane.getClass().equals(Flyer.class)) {
System.out.println("airplane is Flyer class");
}
}
}
輸出
cat is Animal class
cat is Cat class
========================
cat is Cat class
========================
cat is not Dog class
========================
airplane is Airplane class
airplane is Flyer class
========================
airplane is Airplane class
使用instanceof，除了可以得知cat物件屬於Cat類別，也可判斷出cat物件與Animal類別有某種繼承關係。
使用instanceof，也可知道物件與實作類別的關係，像是例子中能知道airplane與Flyer類別有某種繼承或實作關係
使用getClass搭配equals，只能判斷cat物件屬於Cat類別，不能判斷出cat物件與Animal類別有關係
下方為使用instanceof練習寫判斷物件型別的方法
private static void judgeClassByInstanceOf(Object o) {
if (o instanceof String) {
System.out.println(o + " is String type");
} else if (o instanceof Float) {
System.out.println(o + " is Float type");
} else if (o instanceof Double) {
System.out.println(o + " is Double type");
} else if (o instanceof Integer) {
System.out.println(o + " is Integer type");
} else if (o instanceof Boolean) {
System.out.println(o + " is Boolean type");
}
}