7.1 int[][] triArray{	{1},	{1,2},	{1,2,3},};7.2 array[2].length8.1 Unified Modeling Language:UMLUML class diagramCircle_____________radius:double_____________+Circle()+Circle(newRadius:double)getArea():doublecircle1:Circle_________radius = 198.2client8.3reference variableClassName objectRefVar;nullNullPointerException8.4object member access operator:.instance variableinstance methodstatic variable:class variablestatic methodgetter:accessorsetter:mutatorpass by valuecalling object8.5java.util.Date+Date()+Date(elapseTime:long)+toString():String+getTime():long+setTime(elapseTime: long)void8.6java.util.Random+Random()+Random(seed:long)+nextInt():int+nextInt(n:int):int+nextLong():long+nextDouble():double+nextFloat():float+nextBoolean():boolean//Random random1 = new Random(3)8.7javax.swing.JFrameJframe frame1 = new JFrame();frame1.setTitle("Window 1");frame1.setSize(200,150);frame1.setLocation(200,100);frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame1.setVisible(true);JButton jbtOK = new JButton("OK");JLabel jlblName = new JLabel("Enter your name: ");JTextField jtfName = new JTextField("Type in here");JCheckBox jchkBold = new JCheckBox("B");JRadioButton jrbRed = new JRadioButton("Red");JComboBox jcboColor = new JComboBox(new String[]{"freshman","sophomore","junior","senior"});JPanel panel = new JPanel();panel.add(jbtOK);8.8Math.PI8.9package-private:package-accessprivate:类的成员public:类Keyword:accessor method:getter methodactionattributebehaviorclassclientconstructordata fielddate-field encapsulationdefault constructordot operator:object access operatorinstanceinstance methodinstance variableinstantiationmutator method:setternullno-arg constructorobject-oriented programming:OOPUnified Modeling Language:UMLpackage-private:package-accessprivatepropertypublic reference variablereference typestatestatic variablestatic method