为什么Java中可以在不指定类或对象的情况下调用setLayout()？
这是 Java Sound Demo。我的印象是 Java 中的方法总是从对象或类中调用。 setLayout() 方法从何而来？
public class MidiSynth extends JPanel implements ControlContext {
// Fields omitted
public MidiSynth() {
setLayout(new BorderLayout());
JPanel p = new JPanel();
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
EmptyBorder eb = new EmptyBorder(5,5,5,5);
BevelBorder bb = new BevelBorder(BevelBorder.LOWERED);
CompoundBorder cb = new CompoundBorder(eb,bb);
p.setBorder(new CompoundBorder(cb,eb));
JPanel pp = new JPanel(new BorderLayout());
pp.setBorder(new EmptyBorder(10,20,10,5));
pp.add(piano = new Piano());
p.add(pp);
p.add(controls = new Controls());
p.add(new InstrumentsTable());
add(p);
}
This is the beginning of the MidiSynth class from the Java Sound Demo. I was under the impression that methods in Java were always called from an object or a class. Where does the setLayout() method come from here?
public class MidiSynth extends JPanel implements ControlContext {
// Fields omitted
public MidiSynth() {
setLayout(new BorderLayout());
JPanel p = new JPanel();
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
EmptyBorder eb = new EmptyBorder(5,5,5,5);
BevelBorder bb = new BevelBorder(BevelBorder.LOWERED);
CompoundBorder cb = new CompoundBorder(eb,bb);
p.setBorder(new CompoundBorder(cb,eb));
JPanel pp = new JPanel(new BorderLayout());
pp.setBorder(new EmptyBorder(10,20,10,5));
pp.add(piano = new Piano());
p.add(pp);
p.add(controls = new Controls());
p.add(new InstrumentsTable());
add(p);
}
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MidiSynth extends JPanel因此，
setLayout调用实际上是在调用this.setLayoutMidiSynth extends JPanelSo the
setLayoutcall is actually invokingthis.setLayout实际上，因为您的类
MidiSynth继承了JPanel这意味着您可以像处理MidiSynth类的本地方法一样处理所有 JPanel 的方法。Actually, because your class
MidiSynthinheritsJPanelthat means you can deal with all JPanel's methods as you deal with local methods ofMidiSynthclass.此外，
setLayout()是在 java.awt.ContainerAdditionally,
setLayout()is defined in java.awt.Container