Question

如何从通用方法中调用非泛型方法：

    class Test {
        ...
        public <T> int someFunction1(T someParam) {
            return someFunction2(someParam);
        }

        public int someFunction2(String someParam) {
           return 1;
        }

        public int someFunction2(Integer someParam) {
        return 1;
        }
    }

 Test t = new Test;
t.someFunction1(new String("1"));
t.someFunction1(new Integer(5));

是否可以在编译时而不是在运行时执行此操作？

Answer 1

编译器无法确定someParam中的someFunction1是String还是Integer。这样的事情会起作用：

public <T extends String> int someFunction1(T someParam) {
    return someFunction2(someParam);
}

public int someFunction2(String someParam) {
    return 1;
}

如果您希望它为String / Integer，您需要创建一些数据类型或创建someFunction1的重载定义T绑定到Integer }

或者只是一些“丑陋”演员：

public <T> int someFunction1(T someParam) {
    if (someParam instanceof Integer)
        return someFunction2((Integer) someParam);
    else if (someParam instanceof String)
        return someFunction2((String) someParam);
    else throw new IllegalArgumentException("Expected String or Integer")
}

Answer 2

您需要检查参数类型并根据其类型显式转换并调用正确的方法：

public <T> int someFunction1(T someParam) {
    if (someParam instanceof Integer)
        return someFunction2((Integer)someParam);
    else if (someParam instanceof String)
        return someFunction2((String)someParam);
    else
        throw new InvalidArgumentException("Unexepected type: "+someParam.getClass());
}

Answer 3

仿制药不添加任何东西。您可以（并且应该）从方法中删除类型变量而不更改行为：

public int someFunction1(Object someParam) {

然后应用其他答案中提出的if/else instanceof个链之一。

Answer 4

只有当参数始终为字符串或整数

时，此答案才有效

package com.example.android.courtcounter;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.R;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

/**
 * Displays the given score for Team A.
 */
public void displayForTeamA(int score) {
    TextView scoreView = (TextView) findViewById(R.id.team_a_score);
    scoreView.setText(String.valueOf(score));
}
}

如何从通用方法中调用非泛型方法

4 个答案: