新手问题--！！求大神指点！！java代码，错误在哪里？？实在找不出来

[littleshoes]

public class Student {
	private String name;
	private int age;
	private char gender;
	private String phone;
	private String address;
	private String email;
	
	void SetName(String name){
		this.name = name;
	}	
	String GetName(){
		//System.out.println("The Student Name is:" + this.name);
		return this.name;
	}
	
	void SetAge(int age){
		this.age = age;
	}
	int  GetAge(){
		//System.out.println("The Student Age is:" + this.age);
		return this.age;
	}
	
	void SetGender(char gender){
		this.gender = gender;
	}
	char GetGender(){
		//System.out.println("The Student Gender is:" + this.gender);
		return this.gender;
	}
	
	void SetPhone(String phone){
		this.phone = phone;
	}
	String GetPhone(){
		//System.out.println("The Student Phone is:" + this.phone);
		return this.phone;
	}
	
	void SetAddress(String address){
		this.address = address;
	}
	String GetAddress(){
		//System.out.println("The Student Address is:" + this.address);
		return this.address;
	}
	
	void SetEmail(String email){
		this.email = email;
	}
	String GetEmail(){
		//System.out.println("The Student Email is:" + this.email);
		return this.email;
	}
	
	Student(String name, int age, char gender, String phone, String address, String email){
		this.name = name;
		this.age = age;
		this.gender = gender;
		this.phone = phone;
		this.address = address;
		this.email = email;
	}
	
	void Eat(){
		System.out.println(this.GetName() + " is eating!");
	}
	
	void Drink(){
		System.out.println(this.GetName() + " is drinking!");
	}
	
	void Play(){
		System.out.println(this.GetName() + " is playing!");
	}
	
	void Sleep(){
		System.out.println(this.GetName() + " is sleeping!");
	}
}

public class Contact {
	private Student[] contact;
	
	Contact(Student[] contact){
		this.contact = contact;
	}
	
	String QueryByName(String name){
		for(int i = 0; i < this.contact.length; i++){
			if(this.contact[i].GetName() == name)
				return this.contact[i].GetName();
			else
				return "No this Student";
		}
	}
	
	String QueryByEmail(String email){
		for(int i = 0; i < this.contact.length; i++){
			if(this.contact[i].GetEmail() == email)
				return this.contact[i].GetEmail();
			else
				return "No this Student";
		}
	}
	
	String QueryByAddress(String address){
		for(int i = 0; i < this.contact.length; i++){
			if(this.contact[i].GetAddress() == address)
				return this.contact[i].GetAddress();
			else
				return "No this Student";
		}
	}
	
	String QueryByPhone(String phone){
		for(int i = 0; i < this.contact.length; i++){
			if(this.contact[i].GetPhone() == phone)
				return this.contact[i].GetPhone();
			else
				return "No this Student";
		}
	}
}

public class Practice {

	/**
	 * @param args
	 */
	
	
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Student stu1 = new Student("Tom", 31, 'M', "13100000000", "Road 1", "[e-mail]");
		Student stu2 = new Student("Jerry", 32, 'F', "13200000000", "Road 2", "[e-mail]");
		Student stu3 = new Student("Steve", 33, 'M', "13300000000", "Road 3", "[e-mail]");
		Student stu4 = new Student("Tiger", 34, 'F', "13400000000", "Road 4", "[e-mail]");
		Student[] c = new Student[]{stu1,stu2,stu3,stu4};
		Contact contact = new Contact(c);
		/*
		for(int i = 0; i < contact.length; i++){
			System.out.println("Student Name is:" + contact[i].GetName() + "; Address is:" + contact[i].GetAddress() + "; Phone is:" + contact[i].GetPhone());
		}
		*/
		
		contact.QueryByName("Tom");
		contact.QueryByEmail("[e-mail]");
		contact.QueryByAddress("Road 3");
		contact.QueryByPhone("13300000000");
		
	}

}

运行出现以下错误：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	This method must return a result of type String

	at Contact.QueryByName(Contact.java:9)
	at Practice.main(Practice.java:25)

我用的是Myeclips10，jre 1.8.0_60

[gzcitizeny]

根据错误提示，以下行出错。 for(int i = 0; i < this.contact.length; i++){ 和 contact.QueryByAddress("Road 3");

[爱睡觉的阿狸]

Contact里面的四个方法写的都有问题，你应该在for循环体后面再加一个return ...;才对，因为编译器会判断出你很可能进入不了for循环体中，那么你后面没有return语句的话，就不符合这个方法必须返回个字符串类型对象的要求了，所以编译时就会出错。

[ryuugu_rena]

at Contact.QueryByName(Contact.java:9) 第9行出问题了，字符串的比较用equals，用什么==

[鬼善]

数组可以Student[]定义吗！换成arraylist[student] 应该就行了！

[chongchong517]

ceshi

[littleshoes]

引用 3 楼 ryuugu_rena 的回复:

at Contact.QueryByName(Contact.java:9) 第9行出问题了，字符串的比较用equals，用什么==

very 感谢

[littleshoes]

引用 2 楼 m2200 的回复:

Contact里面的四个方法写的都有问题，你应该在for循环体后面再加一个return ...;才对，因为编译器会判断出你很可能进入不了for循环体中，那么你后面没有return语句的话，就不符合这个方法必须返回个字符串类型对象的要求了，所以编译时就会出错。

very感谢

[___d]

字符串比较用equals, 因为你用的==导致没走return，方法没return 就报这个错了

[pake_2016]

建议楼主写代码的时候把修饰符都写上，要不然看的很别扭

[逸花城]

你的逻辑错误，应该这样写！

String QueryByName(String name){
	for(int i = 0; i < this.contact.length; i++){
    	if(this.contact[i].GetName().equals(name)){
        	return this.contact[i].GetName();
        }
    }
    return "No this Student";
}