1.class Test { int a; public int b; private int c; public void setc(int i) { c = i; } public int getc() { return c; } } class AccessTest { public static void main(String args[]) { Test obj = new Test(); obj.a = 10; obj.b = 20; obj.setc(100); System.out.println("a，b，and c: " + obj.a + " " + obj.b + " " + obj.getc()); } } 运行结果：

输出结果为：a，b，and c: 10 20 100

解释：AccessTest 类中创建了 Test 类的实例 obj，并分别给 a、b、c 赋值。因为 a、b 都是 public 类型，所以可以直接访问并赋值。而 c 是 private 类型，不能直接访问，需要通过 setc 和 getc 方法来访问。最后，输出 a、b、c 的值。其中，a 和 b 的值分别为 10 和 20，c 的值为 100，说明 setc 方法设置 c 的值成功。

相关问题

public class TestClock extends JFrame { private String AorP; private String hour; private String minute; private String second; public TestClock() { this.setSize(1000, 800); this.setVisible(true); this.setDefaultCloseOperation(EXIT_ON_CLOSE); this.setLayout(new GridLayout(2, 1)); Panel p1 = new Panel(new GridLayout(1, 3)); while (true) { Calendar c = Calendar.getInstance(); hour = Integer.toString(c.get(Calendar.HOUR)); minute = Integer.toString(c.get(Calendar.MINUTE)); second = Integer.toString(c.get(Calendar.SECOND)); AorP = Integer.toString(c.get(Calendar.AM_PM)); JLabel HH = new JLabel(hour, SwingConstants.CENTER); JLabel MM = new JLabel(minute, SwingConstants.CENTER); JLabel SS = new JLabel(second, SwingConstants.CENTER); JLabel AorP = new JLabel("AM/PM", SwingConstants.CENTER); HH.setFont(new Font(Font.SERIF, Font.ITALIC, 36)); MM.setFont(new Font(Font.SERIF, Font.ITALIC, 36)); SS.setFont(new Font(Font.SERIF, Font.ITALIC, 36)); AorP.setFont(new Font(Font.SERIF, Font.ITALIC, 26)); p1.add(HH); p1.add(MM); p1.add(SS); this.add(p1); this.add(AorP); } } public static void main(String[] args) { // TODO Auto-generated method stub TestClock clock = new TestClock(); } }为什么不显示

这段代码可能会导致程序卡死，因为while(true)会让程序无限循环下去，而且在while循环中不断地创建和添加标签，可能会导致内存溢出。这会导致程序无法正常运行，因此窗口不会显示。

如果想要实现一个实时显示当前时间的时钟，可以使用Timer类来实现。Timer类可以在指定时间间隔内重复执行指定任务，这样就可以实现每隔一段时间更新一次时钟的效果。具体实现可以参考以下代码：

import java.awt.Font;
import java.awt.GridLayout;
import java.util.Calendar;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.Timer;

public class TestClock extends JFrame {
    private JLabel hourLabel;
    private JLabel minuteLabel;
    private JLabel secondLabel;
    private JLabel amPmLabel;

    public TestClock() {
        this.setSize(300, 150);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setLayout(new GridLayout(2, 1));

        JPanel timePanel = new JPanel(new GridLayout(1, 3));
        hourLabel = new JLabel("00", SwingConstants.CENTER);
        minuteLabel = new JLabel("00", SwingConstants.CENTER);
        secondLabel = new JLabel("00", SwingConstants.CENTER);
        timePanel.add(hourLabel);
        timePanel.add(minuteLabel);
        timePanel.add(secondLabel);
        this.add(timePanel);

        amPmLabel = new JLabel("AM", SwingConstants.CENTER);
        amPmLabel.setFont(new Font(Font.SERIF, Font.ITALIC, 24));
        this.add(amPmLabel);

        Timer timer = new Timer(1000, e -> {
            Calendar calendar = Calendar.getInstance();
            int hour = calendar.get(Calendar.HOUR_OF_DAY);
            int minute = calendar.get(Calendar.MINUTE);
            int second = calendar.get(Calendar.SECOND);
            String amPm = hour < 12 ? "AM" : "PM";
            hour = hour % 12;
            hourLabel.setText(String.format("%02d", hour));
            minuteLabel.setText(String.format("%02d", minute));
            secondLabel.setText(String.format("%02d", second));
            amPmLabel.setText(amPm);
        });
        timer.start();
    }

    public static void main(String[] args) {
        TestClock clock = new TestClock();
        clock.setVisible(true);
    }
}

这个时钟每隔1秒更新一次，实时显示当前时间。注意，这里用到了Java 8中的Lambda表达式来简化代码。

package main.mymath; import java.util.InputMismatchException; import java.util.Scanner; public class MyCalculator { //Addition public void add(int num1,int1 num2) { int result; result = num1 + num2; if(result > Integer.MAX_VALUE || result < Integer.MIN_VALUE){ throw new IllegalArgumentException("输入数字导致溢出"); }else { System.out.println(result); } } //Multiplication public void subtraction(double num1,double num2) { System.out.println(num1 - num2); } //Division public void divide(double num1,double num2) { if(num2==0) { throw new IllegalArgumentException("分母不能为零"); }else { System.out.println(num1 / num2); } } public void calc() { Scanner sc = new Scanner(System.in); System.out.println("premier nombre："); int num1 = sc.nextInt(); System.out.println("deuxieme nombre："); int num2 = sc.nextInt(); System.out.println("choix【+，-，/】"); char op = sc.next().charAt(0); switch (op) { case '+': add(num1, num2); break; case '-': subtraction(num1, num2); break; case '/': divide(num1, num2); break; default: System.out.println("erreur！"); break; } } public static void main(String[] args) { MyCalculator c = new MyCalculator(); c.calc(); } }

好的，根据你提供的代码，以下是一个可能的测试类示例：

package test.mymath;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThrows;
import java.io.ByteArrayInputStream;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.util.Scanner;
import org.junit.Before;
import org.junit.Test;
import main.mymath.MyCalculator;

public class MyCalculatorTest {

    private MyCalculator calculator;

    @Before
    public void setUp() {
        calculator = new MyCalculator();
    }

    @Test
    public void testAdd() {
        assertEquals(5, calculator.add(2, 3));
        assertEquals(-1, calculator.add(2, -3));
        assertEquals(0, calculator.add(0, 0));
        assertThrows(IllegalArgumentException.class, () -> calculator.add(Integer.MAX_VALUE, 1));
    }

    @Test
    public void testSubtraction() {
        assertEquals(2.0, calculator.subtraction(5.0, 3.0), 0.0);
        assertEquals(-2.0, calculator.subtraction(-5.0, -3.0), 0.0);
        assertEquals(0.0, calculator.subtraction(0.0, 0.0), 0.0);
        assertEquals(0.1, calculator.subtraction(0.3, 0.2), 0.0);
    }

    @Test
    public void testDivide() {
        assertEquals(2.0, calculator.divide(6.0, 3.0), 0.0);
        assertEquals(-2.0, calculator.divide(6.0, -3.0), 0.0);
        assertEquals(0.0, calculator.divide(0.0, 1.0), 0.0);
        assertThrows(IllegalArgumentException.class, () -> calculator.divide(6.0, 0.0));
    }

    @Test
    public void testCalc() {
        String input = "2\n3\n+\n";
        System.setIn(new ByteArrayInputStream(input.getBytes()));
        Scanner scanner = new Scanner(System.in);
        calculator.calc(scanner);
        assertEquals("5\n", systemOut().getHistory());

        input = "5.0\n3.0\n-\n";
        System.setIn(new ByteArrayInputStream(input.getBytes()));
        scanner = new Scanner(System.in);
        calculator.calc(scanner);
        assertEquals("2.0\n", systemOut().getHistory());

        input = "4.0\n2.0\n/\n";
        System.setIn(new ByteArrayInputStream(input.getBytes()));
        scanner = new Scanner(System.in);
        calculator.calc(scanner);
        assertEquals("2.0\n", systemOut().getHistory());
    }

    @Test
    public void testCalcInvalidInput() {
        String input = "invalid\ninput\n";
        System.setIn(new ByteArrayInputStream(input.getBytes()));
        Scanner scanner = new Scanner(System.in);
        assertThrows(NoSuchElementException.class, () -> calculator.calc(scanner));
    }

    private SystemOut systemOut() {
        return new SystemOut();
    }

    private static class SystemOut extends java.io.ByteArrayOutputStream {
        public String getHistory() {
            return new String(this.toByteArray());
        }
    }
}

在上面的测试类示例中，我们使用JUnit框架来测试MyCalculator类的三个方法：add()，subtraction()和divide()，并使用标准输入输出模拟用户交互，测试calc()方法是否能够正确的计算加、减、除三种运算。同时，我们还测试了一些输入无效数据的情况，来保证程序的健壮性。