英文:
Getting Null when calling variable from another class
问题
我已经对此进行了大量的Google搜索，并尝试了许多方法，但从未成功。所以我有一个在Class A中的变量，并且我想在Class B中打印该变量，但在调用该变量之前，Class A中的变量的值会经过一个方法。
public class TestSubject extends javax.swing.JFrame {
static String a;
private void testButtonActionPerformed(java.awt.event.ActionEvent evt) {
a = "hello"; }
}
在这里，我声明了变量并点击按钮将变量的值设置为'hello'。我通过在同一类中有另一个按钮来打印变量'a'来测试变量是否确实获得了值。
public class TestSubject2 extends javax.swing.JFrame {
TestSubject test = new TestSubject();
private void okActionPerformed(java.awt.event.ActionEvent evt) {
System.out.println(test.a);
}
}
所以在这里，我尝试从类'TestSubject'中打印变量'a'。
所以我尝试过：
我尝试使用非静态和静态两种方式。
我尝试使用返回方法
class TestSubject { //故意留下了扩展，但你知道我的意思
public String getString() {
return a; } }
Class TestSubject2 {
TestSubject test = new TestSubject();
private void okActionPerformed(java.awt.event.ActionEvent evt) {
System.out.println(test.getString());
}
}
然而，如果我明确为'a'赋一个值，比如：
static String a = "hello";
它将使用第一种方法在另一个类中正确打印出来。
我确保按顺序点击按钮以输入值。
所以我想知道的是如何从另一个类中调用变量。
英文:
I have done a lot of google regarding this and tried many things and have never gotten through. So I have this variable in Class A and I want to print that variable in Class B but the value of the variable in Class A goes through a method before it is called.
public class TestSubject extends javax.swing.JFrame {
static String a;
private void testButtonActionPerformed(java.awt.event.ActionEvent evt) {
a = "hello"; }
}
Here I declare the variable and clicks a button to set the variable value to 'hello'. I tested if the variable did indeed get the value by having another button printing the variable 'a' in the same class.
public class TestSubject2 extends javax.swing.JFrame {
TestSubject test = new TestSubject();
private void okActionPerformed(java.awt.event.ActionEvent evt) {
System.out.println(test.a);
}
}
So here I try print the variable a from class 'TestSubject'.
So what I have tried:
I have tried to use both non-static and static.
I have tried to use a return method
class TestSubject { //purposely left the extend but you get what I mean
public String getString() {
return a; } }
Class TestSubject2 {
TestSubject test = new TestSubject();
private void okActionPerformed(java.awt.event.ActionEvent evt) {
System.out.println(test.getString());
}
}
However, if I were to explicitly give 'a' a value like:
static String a = "hello";
It would print out properly in the other class using the first method.
I made sure I click the buttons sequentially so the values are being inputted.
So what I want to know is how can I call a variable from another class.
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