[Java]Generics(泛型)

在Java中,有時候會遇到邏輯相似但型態可能不同的類別

例如:
test1.java

package mypackage;
public class test1 {
    private int num;
    public void setVal(int num) {
        this.num = num;
    }

    public int getVal() {
        return this.num;
    }
}

test2.java

package mypackage;
public class test2 {
    private String str;
    public void setVal(String str) {
        this.str = str;
    }

    public String getVal() {
        return this.str;
    }
}

index.java

import mypackage.test1;
import mypackage.test2;
public class index {
    public static void main(String[] argv) {
        test1 t1 = new test1();
        test2 t2 = new test2();

        t1.setVal(123);
        System.out.println(t1.getVal());
        t2.setVal("This is test");
        System.out.println(t2.getVal());
    }
}

上面範例除了還要再新增一個class之外,如果遇到後續邏輯修改,也要重複將類似邏輯的class修完,非常的浪費時間

這時候使用泛型就可以解決上述的問題

generics.java

package mypackage;
public class generics<T> {
    private T val;
    public void setVal(T val) {
        this.val = val;
    }

    public T getVal() {
        return this.val;
    }
}

index.java

import mypackage.generics;
public class index {
    public static void main(String[] argv) {
        generics<Integer> t1 = new generics<Integer>();
        generics<String> t2 = new generics<String>();

        t1.setVal(123);
        System.out.println(t1.getVal());
        t2.setVal("This is test");
        System.out.println(t2.getVal());
    }
}

另外也可以限制泛型的類別,限制可以使用的類別()

package mypackage;
public class generics<T extends List> {
    //d這樣只能使用像ArrayList、LinkedList等型別
}

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