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当我尝试调用方法参数中的布尔数组时,我在我的程序中出现nullPointerException。布尔数组被创建为常量,然后在单独的void方法中初始化。有人可以向我解释为什么它找不到布尔数组(或无法找到数组值)?如何初始化数组以避免空指针异常?
public static void moveTarget(Graphics g) {
if (!targetMovement)
return;
drawTarget(g, BACKGROUND_COLOR);
drawShield(g, BACKGROUND_COLOR);
这条线就在这里是程序失败的具体部分。 (nullPointerException)
int f = findTargetMissilePosition(targetMissileActive);
我在这里指定常量,但不要初始化。
// Target Missile values
public static Color TARGET_MISSILE_COLOR = TARGET_COLOR;
public static int MAX_MISSILES = 10;
public static double TARGET_MISSILE_SPEED = MISSILE_SPEED;
public static double TARGET_SHOOT_PROBABILITY = .1;
public static double[] targetMissilePositionX;
public static double[] targetMissilePositionY;
public static double[] targetMissileDeltaX;
public static double[] targetMissileDeltaY;
public static boolean[] targetMissileActive;
// main method does initialization and calls startGrame
public static void main(String[] args) {
DrawingPanel panel = new DrawingPanel(PANEL_WIDTH, PANEL_HEIGHT);
Graphics g = panel.getGraphics();
initialize();
startGame(panel, g);
} //初始化()被调用以上是其中阵列intialized
// start the main game loop which runs forever
public static void startGame(DrawingPanel panel, Graphics g) {
while(true) {
panel.sleep(SLEEP_TIME);
handleKeys(panel,g);
moveTarget(g);
drawAll(g);
moveMissile(g);
shootTargetMissile(g);
for (int i=0;i<10;i++) {
int f = findTargetMissilePosition(targetMissileActive);
moveTargetMissile(g, f);
}
shieldHitTimer--;
targetHitTimer--;
shooterHitTimer--;
}
} //上述是第一次的代码行出现和不出现有问题。
// reset all parameters to start over
public static void reset(Graphics g) {
g.setColor(BACKGROUND_COLOR);
g.fillRect(0,0,PANEL_WIDTH,PANEL_HEIGHT);
initialize();
}
//Here the arrays are initialized
// initialize parameters for the start of the program
public static void initialize() {
shooterPositionX = SHOOTER_INITIAL_POSITION_X;
gunAngle = 0;
targetPositionX = PANEL_WIDTH/2;
missileActive = false;
hitCount = 0;
shooterHitCount = 0;
hitDisplayString = "Hits: ";
targetDeltaX = 0;
targetHitTimer = 0;
shieldHitTimer = 0;
shooterHitTimer = 0;
boolean [] targetMissileActive = new boolean [9]; // might change??
int [] targetMissilePositionX = new int [9];
int [] targetMissilePositionY = new int [9];
int [] targetMissileDeltaX = new int [9];
int [] targetMissileDeltaY = new int [9];
for (int i=0; i<9; i++) {
targetMissilePositionX[i] = 0;
targetMissilePositionY[i] = 0;
targetMissileDeltaX[i] = 0;
targetMissileDeltaY[i] = 0;
targetMissileActive[i] = false;
}
}
// draw everything in its current position
public static void drawAll(Graphics g) {
g.setColor(Color.BLACK);
g.drawString("Project 3 by Benjamin Koch",10,15);
g.drawString(hitDisplayString,10,30);
int f = findTargetMissilePosition(targetMissileActive);
drawTargetMissile(g, TARGET_MISSILE_COLOR, f);
drawShooter(g,SHOOTER_COLOR);
if (targetHitTimer > 0)
drawTarget(g, SHIELD_HIT_COLOR);
else
drawTarget(g,TARGET_COLOR);
Color shieldColor = BACKGROUND_COLOR; // default: do not draw
if (shieldActive) {
if (shieldHitTimer > 0)
shieldColor = SHIELD_HIT_COLOR;
else
shieldColor = SHIELD_COLOR;
}
drawShield(g, shieldColor);
}
public static int findTargetMissilePosition (boolean[] data) {
for (int i=0;i<MAX_MISSILES;i++) {
if (data[i]==false) {
return i;
}
}
return -1;
}
你正在初始化一个局部变量,其名称与静态全局变量不同。要解决这个问题,你可能想把它改成像“ClassName.targetMissilesActive = new boolean [9]”等等。 – Steven
我试图初始化布尔数组(并且我把它写成了整数和新数组)。谢谢! – TheAeroHead
初始化静态字段的一个很好的做法是创建一个静态块。 http://beginnersbook.com/2013/04/java-static-class-block-methods-variables/以供参考。 – Steven