为什么我会收到此错误？ “二元运算符“&&”的操作数类型错误 第一种类型：int 第二种类型：布尔值

Question

I don't see why I would get this error because there is no boolean given, I gave 2 integers but it still tells me that there's an error.

Here's my code:

import java.util.Scanner;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
class MainMenu
{

JFrame frame= new JFrame();
JFrame frame2 = new JFrame();
JFrame frame3 = new JFrame();
JButton button = new JButton("Singleplayer");
JButton button2 = new JButton("Multiplayer");
JButton b = new JButton("Submit");
JLabel label = new JLabel(" ");
int i;
int i2;
MainMenu(){
    prepareGUI();
}  

public void prepareGUI(){
    frame.setTitle("Game");
    frame.getContentPane().setLayout(null);
    frame.add(button);
    frame.add(button2);
    button.setBounds(100,200,100,40);
    button2.setBounds(200,200,100,40);
    frame.setVisible(true);
    frame.setBounds(200,200,400,400);
    frame2.getContentPane().setLayout(null);
    frame2.setBounds(200,200,400,400);
    frame2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame3.getContentPane().setLayout(null);
    frame3.setBounds(200,200,400,400);
    frame3.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    ActionListener buttonlistener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                frame2.setTitle("Multiplayer");
                frame2.setVisible(true);
                JLabel labelM = new JLabel("Geben sie eine Höhstzahl ein:");
                JTextField hZahl = new JTextField();
                JLabel labelN= new JLabel("Mit wie vielen Rateversuchen wollen sie `spielen?");`
                JTextField rVers = new JTextField();
                JButton b = new JButton("Submit");
                labelM.setBounds(50, 50, 400, 70);
                labelN.setBounds(50, 105, 400, 70);
                rVers.setBounds(45, 150, 100, 30);
                hZahl.setBounds(45, 95, 100, 30);
                b.setBounds(150,250,100,40);
                frame2.add(b);
                frame2.add(hZahl);
                frame2.add(labelM);
                frame2.add(labelN);
                frame2.add(rVers);

                hZahl.addActionListener(new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent event) {
                            System.out.println("The entered text is: " + hZahl.getText());
                            int i = Integer.parseInt(hZahl.getText());
                            System.out.println(i);
                        }
                    });
                rVers.addActionListener(new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent event) {
                            System.out.println("The entered text is: " + rVers.getText());
                            int i2 = Integer.parseInt(rVers.getText());
                            System.out.println(i2);
                        }
                    });
                ActionListener buttonlistener3 = new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent ae) { 
                            frame3.setTitle("1 Player Game");
                            frame3.setVisible(true);
                        }
                    };
                b.addActionListener(buttonlistener3);
            }
        };

    ActionListener buttonlistener2 = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                //frame.getContentPane().setBackground(Color.red);
                //System.out.println("Multiplayer Selected");
                frame2.setTitle("Multiplayer");
                frame2.setVisible(true);
                JLabel labelM = new JLabel("Geben sie eine Höhstzahl ein:");
                JTextField hZahl = new JTextField();
                JLabel labelN= new JLabel("Mit wie vielen Rateversuchen wollen sie spielen?");
                JTextField rVers = new JTextField();
                JButton b = new JButton("Submit");
                labelM.setBounds(50, 50, 400, 70);
                labelN.setBounds(50, 105, 400, 70);
                rVers.setBounds(45, 150, 100, 30);
                hZahl.setBounds(45, 95, 100, 30);
                b.setBounds(150,250,100,40);
                frame2.add(b);
                frame2.add(hZahl);
                frame2.add(labelM);
                frame2.add(labelN);
                frame2.add(rVers);

                hZahl.addActionListener(new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent event) {
                            System.out.println("The entered text is: " + hZahl.getText());
                            int i = Integer.parseInt(hZahl.getText());
                            System.out.println(i);
                        }
                    });
                rVers.addActionListener(new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent event) {
                            System.out.println("The entered text is: " + rVers.getText());
                            int i2 = Integer.parseInt(rVers.getText());
                            System.out.println(i2);
                        }
                    });
                ActionListener buttonlistener3 = new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent ae) { 
                            if(i && i2 < 0){
                            frame3.setTitle("2 Player Game");
                            frame3.setVisible(true);
                        }
                        }
                    };
                b.addActionListener(buttonlistener3);
            }
        };
    

I am unsure as to why this is happening because as far as I am concerned I did not use a single boolean, and both i and i2 are separately and clearly marked as integers. The error message appears here:

if(i && i2 < 0){
      frame3.setTitle("2 Player Game");
      frame3.setVisible(true);
                        }

Thank you in advance!

Answer 1

The < operator has more precedence than the && operator. Hence your statement will be computed as i && (i2 < 0) . In this case i2 < 0 will be a boolean and i is an integer.

To solve this issue use the brackets as

(i < 0) && (i2 < 0)