Question

import java.util.Scanner; public class test3_2 { /** * @param args */ public static void main(Strin

运行不出来，为什么？求解 谢谢(*^__^*)
import java.util.Scanner;

public class test3_2 {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc=new Scanner(System.in);
String grade=sc.next();
if(grade=="A")
System.out.println(grade+" is 85~100");
else if(grade=="B")
System.out.println(grade+" is 70~84");
else if(grade=="C")
System.out.println(grade+" is 60~69");
else if(grade=="D")
System.out.println(grade+" is <60");
}

}

Answer 1

import java.util.Scanner;

public class ScannerTest {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String grade = sc.next();
if ("A".equals(grade))
System.out.println(grade + " is 85~100");
else if ("B".equals(grade))
System.out.println(grade + " is 70~84");
else if ("C".equals(grade))
System.out.println(grade + " is 60~69");
else if ("D".equals(grade))
System.out.println(grade + " is <60");
}

}
对象比较的时候，用equals()
顺便说一下，用 "A".equals(grade) 和 grade.equals("A"); 使用前者的形式，因为当 grade ==null 时，前者不会有异常，而后者有异常。

Answer 2

if判断里的条件全部改成 "A".equals(grade) 这种形式， 字符串不能拿==判断。