Java 得到一个;找不到符号“;抽象类错误
这是给我的大学班级的 我有一个顶级抽象类Expression.java(由教授提供): BinaryExpression.java(也由教授提供),它扩展了Expression.java:Java 得到一个;找不到符号“;抽象类错误,java,Java,这是给我的大学班级的 我有一个顶级抽象类Expression.java(由教授提供): BinaryExpression.java(也由教授提供),它扩展了Expression.java: public abstract class BinaryExpression extends Expression { protected Expression left; protected Expression right; public BinaryExpression (E
public abstract class BinaryExpression extends Expression {
protected Expression left;
protected Expression right;
public BinaryExpression (Expression l, Expression r) {
left = l;
right = r;
}
public abstract int eval();
public abstract String toString();
}
public class Add extends BinaryExpression {
//Fields
protected Expression left;
protected Expression right;
//Constructor
public Add(Expression l, Expression r) {
left = l;
right = r;
}
//Methods
public int eval() {
return left.eval()+right.eval();
}
public String toString() {
return left + "+" + right;
}
}
最后,Add.java(我写了这个)扩展了BinaryExpression.java:
public abstract class BinaryExpression extends Expression {
protected Expression left;
protected Expression right;
public BinaryExpression (Expression l, Expression r) {
left = l;
right = r;
}
public abstract int eval();
public abstract String toString();
}
public class Add extends BinaryExpression {
//Fields
protected Expression left;
protected Expression right;
//Constructor
public Add(Expression l, Expression r) {
left = l;
right = r;
}
//Methods
public int eval() {
return left.eval()+right.eval();
}
public String toString() {
return left + "+" + right;
}
}
测试人员Test.java也提供了。还有另外三个类扩展了BinaryExpression、减法、乘法和除法,但它们实际上与加法相同。加号和减号只存储一个值,可以是负数也可以是正数
public class Test {
public static void main (String [] args) {
Expression s1 = new SimpleExpression(10);
Expression s2 = new SimpleExpression(-3);
System.out.println("s1: " + s1 + " = " + s1.eval());
System.out.println("s2: " + s2 + " = " + s2.eval());
Expression u1 = new Plus(s2);
Expression u2 = new Minus(s1);
System.out.println("u1: " + u1 + " = " + u1.eval());
System.out.println("u2: " + u2 + " = " + u2.eval());
Expression b1 = new Add(u1, s2);
Expression b2= new Subtract(s1, u2);
Expression b3= new Multiply(u1, b1);
Expression b4= new Divide(u2, b3);
System.out.println("b1: " + b1 + " = " + b1.eval());
System.out.println("b2: " + b2 + " = " + b2.eval());
System.out.println("b3: " + b3 + " = " + b3.eval());
System.out.println("b4: " + b4 + " = " + b4.eval());
Expression e = new Minus( new Multiply(b3, b2));
System.out.println("e: " + e + " = " + e.eval());
// example given in the assignment
e = new Divide(new Add(new Minus(new SimpleExpression (10)),
new SimpleExpression (50)),
new Minus(new Multiply(new SimpleExpression(5),
new Minus (new SimpleExpression (3)))));
System.out.println("Another e: " + e + " = " + e.eval());
}
}
当我编译Test.java时,我得到了这个错误(还有一个类似的减法、乘法和除法错误):
发生了什么事?根本原因就在这里
public Add(Expression l, Expression r) {
left = l;
right = r;
}
您的子类正在尝试隐式调用无参数超级构造函数。父类没有这样的无参数构造函数。因此,请调用其现有构造函数
public Add(Expression l, Expression r) {
super(l, r);
left = l;
right = r;
}
另外,您正在重新说明Add
类中的left
和right
字段。这样做没有意义。您的子类已经可以访问其父类的left
和right
字段,BinaryExpression
根本原因在这里
public Add(Expression l, Expression r) {
left = l;
right = r;
}
您的子类正在尝试隐式调用无参数超级构造函数。父类没有这样的无参数构造函数。因此,请调用其现有构造函数
public Add(Expression l, Expression r) {
super(l, r);
left = l;
right = r;
}
另外,您正在重新说明Add
类中的left
和right
字段。这样做没有意义。您的子类已经可以访问其父类的left
和right
字段BinaryExpression