如何编写泛型

第一步，编写类

public class Animal {
    private String name;
    private String type;

    public Animal(String name, String type) {
        this.name = name;
        this.type = type;
    }

    public String getName() {
        return name;
    }

    public String getType() {
        return type;
    }
}

第二步，把特定类型 String 替换为 T，并声明 <T>

public class Animal<T> {
    private T name;
    private T type;

    public Animal(T name, T type) {
        this.name = name;
        this.type = type;
    }

    public T getName() {
        return name;
    }

    public T getType() {
        return type;
    }
}

熟练之后可以直接写第二步

静态方法

编写泛型类时，泛型类型 <T> 不能用于静态方法，下述代码会导致编译错误

public class Animal<T> {
    private T name;
    private T type;

    public Animal(T name, T type) {
        this.name = name;
        this.type = type;
    }
    ......

    public static <T> Animal<T> run(T name, T type) {
        return new Animal<T>(name, type);
    }
}

我们在 static 修饰符后面加一个 <T>，编译就能通过

public class Animal<T> {
    private T name;
    private T type;

    public Animal(T name, T type) {
        this.name = name;
        this.type = type;
    }
    ......

    public static <T> Animal<T> run(T name, T type) {
        return new Animal<T>(name, type);
    }
}

实际上，这里的 T 和 Animal<T> 类型的 <T> 没有任何关系，所以我们把静态方法改成另一种泛型类型，比如 <K>

public class Animal<T> {
    private T name;
    private T type;

    public Animal(T name, T type) {
        this.name = name;
        this.type = type;
    }
    ......

    public static <K> Animal<K> run(K name, K type) {
        return new Animal<K>(name, type);
    }
}

多个泛型类型

泛型还可以定义多种类型

public class Animal<T, K> {
    private T name;
    private K type;

    public Animal(T name, K type) {
        this.name = name;
        this.type = type;
    }

    public T getName() {
        return name;
    }

    public K getType() {
        return type;
    }
}