package test;

import java.util.Scanner;

public class Test28 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //只能判断正整数奇偶，负数都显示偶数
        method1(scanner);
        //负数也可以判断奇偶
        //method2(scanner);
        //负数也可以判断奇偶，位操作，速度最快
        //method3(scanner);
    }

    private static void method1(Scanner scanner) {
        while (true) {
            System.out.println("method 1 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if (input % 2 == 1) {
                System.out.println("奇数");
            } else {
                System.out.println("偶数");
            }
        }
    }

    private static void method2(Scanner scanner) {
        while (true) {
            System.out.println("method 2 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if (input % 2 != 0) {
                System.out.println("奇数");
            } else {
                System.out.println("偶数");
            }
        }
    }

    private static void method3(Scanner scanner) {
        while (true) {
            System.out.println("method 3 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if ((input & 1) == 1) {
                System.out.println("奇数");
            } else {
                System.out.println("偶数");
            }
        }
    }
}

如果method1不做任何处理，则

private static void method1(Scanner scanner) {
        while (true) {
            System.out.println("method 1 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if (input % 2 == 1) {
                System.out.println("奇数");
            }
            if (input % 2 == 0) {
                System.out.println("偶数");
            }
        }
    }

当输入0时结束判断，进入下一个方法，0的奇偶判断也会做的，3个方法循环判断

package test;

import java.util.Scanner;

public class Test28 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //只能判断正整数奇偶，负数都显示偶数
        method1(scanner);
        //负数也可以判断奇偶
         method2(scanner);
        //负数也可以判断奇偶，位操作，速度最快
        method3(scanner);
    }

    private static void method1(Scanner scanner) {
        while (true) {
            System.out.println("method 1 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if (input % 2 == 1) {
                System.out.println("奇数");
            }
            if (input % 2 == 0) {
                System.out.println("偶数");
            }
            if (input==0){
                break;
            }
        }
    }

    private static void method2(Scanner scanner) {
        while (true) {
            System.out.println("method 2 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if (input % 2 != 0) {
                System.out.println("奇数");
            } else {
                System.out.println("偶数");
            }
            if (input==0){
                break;
            }
        }
    }

    private static void method3(Scanner scanner) {
        while (true) {
            System.out.println("method 3 ");
            System.out.println("INPUT NUMBER : ");
            int input = scanner.nextInt();
            if ((input & 1) == 1) {
                System.out.println("奇数");
            } else {
                System.out.println("偶数");
            }
            if (input==0){
                break;
            }
        }
    }


}